Fourier-transform microwave spectrum, structure, harmonic force field, and hyperfineconstants of sulfur chloride fluoride, ClSFJürgen Preusser and Michael C. L. Gerry Citation: The Journal of Chemical Physics 106, 10037 (1997); doi: 10.1063/1.474061 View online: http://dx.doi.org/10.1063/1.474061 View Table of Contents: http://scitation.aip.org/content/aip/journal/jcp/106/24?ver=pdfcov Published by the AIP Publishing Articles you may be interested in Fourier-transform microwave spectroscopy of the CCCCl radical J. Chem. Phys. 130, 094302 (2009); 10.1063/1.3084954 Fourier transform microwave spectroscopy of HSiBr: Exploring the Si–Br bond through quadrupole hyperfinecoupling J. Chem. Phys. 122, 214314 (2005); 10.1063/1.1926284 Fourier transform microwave spectroscopy and Fourier transform microwave–millimeter wave double resonancespectroscopy of the ClOO radical J. Chem. Phys. 121, 8351 (2004); 10.1063/1.1792591 The molecular properties of chlorosyl fluoride, FClO, as determined from the ground-state rotational spectrum J. Chem. Phys. 116, 2407 (2002); 10.1063/1.1433002 Fourier transform microwave spectroscopy of the 2 Σ + ground states of YbX (X=F, Cl, Br): Characterization ofhyperfine effects and determination of the molecular geometries J. Chem. Phys. 115, 6979 (2001); 10.1063/1.1404146

This article is copyrighted as indicated in the article. Reuse of AIP content is subject to the terms at: http://scitation.aip.org/termsconditions. Downloaded to IP:

155.247.166.234 On: Sat, 22 Nov 2014 10:03:48

Fourier-transform microwave spectrum, structure, harmonic force field,and hyperfine constants of sulfur chloride fluoride, ClSF

Jurgen Preusser and Michael C. L. GerryDepartment of Chemistry, The University of British Columbia, 2036 Main Mall,Vancouver B.C. V6T 1Z1, Canada

~Received 3 March 1997; accepted 14 March 1997!

The rotational spectrum of sulfur choride fluoride, ClSF, has been observed for the first time in thefrequency range 8–26 GHz by means of a pulsed molecular jet Fourier-transform microwavespectrometer. The unstable sample molecule has been prepared using a pulsed electrical dischargein jets containing a mixture of SF6 and SCl2 in Ne. Besides the parent species35Cl32S19F, theisotopomers37Cl32S19F and35Cl34S19F could be observed in natural abundance. Rotational constantsand quartic centrifugal distortion constants as well as nuclear quadrupole coupling constants due to35Cl and37Cl and spin–rotation constants due to35Cl, 37Cl, and19F are given. The data were usedfor the determination ofr 0 , rDP , r s structural parameters. Additionally, the new data were used forthe refinement of the molecular harmonic force field. Results from those harmonic force fieldcalculations were applied in the evaluation of the ground-state average structure,r z , and theestimation of the equilibrium structure,r e . The r s structure is r ~SF!5160.653~162! pm,r ~SCl!5199.437~65! pm, and/~ClSF!5100.732~81!°. The diagonal elements of the35Cl/37Clquadrupole coupling tensors have been obtained, and are interpreted in terms of the bonding at35Cl/37Cl. Negative19F spin–rotation constants suggest a close analogy of the electronic structuresof ClSF and SF2. © 1997 American Institute of Physics.@S0021-9606~97!03323-0#

I. INTRODUCTION

Sulfur dichloride, SCl2, and sulfur difluoride, SF2, areboth well-known species, whose microwave spectra and mo-lecular structures have been known for many years.1–4 Incontrast, there is very little information on the mixed sulfurchloride fluoride, ClSF, available in the literature. To ourknowledge the only experimental evidence of the existenceof ClSF is low resolution IR spectra obtained by Willner5

using rare gas matrix isolation. An extensive theoreticalstudy employing density functional methods of various sul-fur chloride fluorides, SFnCl with n51–5, and their corre-sponding anions, by Gutsev and Ziegler,6 provided anabinitio structure for our target molecule.

The microwave spectrum of ClSF is of interest on sev-eral grounds. In the first place, SF2 is a rather unstable tran-sient species, which dimerizes when it condenses.5,7 SCl2, onthe other hand, is readily available commercially as a liquidcontaining the monomer. There was thus a question whetherthe geometry of ClSF could be easily predicted from theknown parameters of SF2. The interest was increased furtherby the recently obtained unusual, negative,19F spin–rotationconstants in SF2.

8 Since these could be rationalized in termsof the molecular electronic structure, we were curiouswhether similar features could be found for ClSF.

This paper presents the rotational spectra of three isoto-pomers of ClSF. They were measured using a Balle–Flygare-type pulsed jet cavity Fourier-transform microwave~FTMW! spectrometer.9 The samples were produced usingan electric discharge apparatus mounted at the front of thesample injection nozzle. This technique has recently beenshown to be ideal for producing small reactive molecules forspectroscopic study.8,10–12 The molecules are produced as

they are needed, and are stabilized in the essentiallycollision-free jet. The amounts of sample produced are verysmall, but enough for spectroscopic study. As anticipated,the technique was ideal for the present work.

The analysis of the spectra has produced accurate rota-tional constants, which have been used to derive the molecu-lar geometry. In addition, experimental centrifugal distortionconstants have been combined with earlier infrared data5 torefine the harmonic force field. The spectra have also pro-vided hyperfine constants~35Cl/37Cl nuclear quadrupole cou-pling constants, and35Cl/37Cl and 19F spin–rotation con-stants! which give some insight into the molecular electronicstructure.

II. EXPERIMENTAL DETAILS

All measurements described in this paper were per-formed in the frequency range of 8–26 GHz, using the cavitypulsed Fourier-transform microwave spectrometer whichwas described earlier.13 In this instrument the sample mol-ecules or its precursors mixed with a large excess of an inertcarrier gas are injected into a microwave Fabry–Perot-typecavity via a supersonic expansion through a General Valvenozzle. Since the nozzle is located near the center of onemirror, the sample-gas jet travels coaxially to the direction ofpropagation of the microwaves. This results in a typical split-ting of each transition into two Doppler components. The~sub-Doppler! widths of single, well-resolved observed linestypically lie between 5 and 10 kHz~full width at half–maximum!. The accuracy of the measured frequencies is bet-ter than61 kHz for lines with a good signal-to-noise ratio~S/N!; it is somewhat lower for weak lines with poor S/N, orfor partially overlapped lines.

10037J. Chem. Phys. 106 (24), 22 June 1997 0021-9606/97/106(24)/10037/11/$10.00 © 1997 American Institute of Physics This article is copyrighted as indicated in the article. Reuse of AIP content is subject to the terms at: http://scitation.aip.org/termsconditions. Downloaded to IP:

155.247.166.234 On: Sat, 22 Nov 2014 10:03:48

The unstable molecule ClSF investigated in this workwas produced by a pulsed electric discharge~5–10 kV! in asmall chamber~5 mm long and 1 mm diam! directly in frontof the nozzle inside the microwave cavity. The dischargeproduces atomic and molecular fragments of the injectedprecursor molecules which then can react in this chamber toproduce the products of interest. The precise setup of thedischarge apparatus used has been described elsewhere.8

In order to produce ClSF we used mixtures of SF6 andCl2, as well as of SF6 and SCl2, in Ne or Ar. The best results~the highest concentration of ClSF in the cavity! were ob-tained using mixtures of 0.5% SF6 and 0.5% SCl2 in approxi-mately 6 bar Ne. Mixtures using SF6 and SCl2 turned out toproduce approximately 2 or 3 times higher concentrations ofClSF than mixtures of SF6 and Cl2 under the same condi-tions. Therefore the former were used for most of the mea-surements. The timing of the discharge relative to the timingof the pulsed nozzle was initially adjusted by monitoringeither the decrease of the intensity of lines of SCl2 or theincrease of the intensity of lines of SF2, which is also pro-duced in these conditions. After the observation of the firstClSF lines, their intensities were used to optimize the ClSFconcentrations in the cavity.

III. OBSERVED SPECTRA AND ANALYSIS

Initially, in order to narrow the frequency search rangeto a reasonable interval, the structure of ClSF was estimatedby averaging ther 0 structures of SCl2 ~Refs. 1 and 2! andSF2.

3,4 This produced bond lengthsr 0 ~SF!5158.7 pm andr 0 ~SCl!5201.4 pm and a bond angle/~ClSF!5100°. Wefurther estimated, from the uncertainties in the geometries ofSF2 and SCl2, that the uncertainties inB andC should beapproximately650 MHz, and inA should be approximately6100 MHz. Theab initio values for ther e structure given byGutsev and Ziegler6 were somewhat different, and the result-ing rotational constants did not fall within our estimated er-ror range. We nevertheless started our search using the esti-mated structure above, because we believed that theab initiobond lengths might be too large. Figure 1 illustrates the ge-ometry of ClSF in its principal axis system, with ther s struc-ture obtained in the present work~see below!.

It was also important initially to have an estimate of the35Cl nuclear quadrupole coupling constant, because it wasexpected to be large enough to cause hyperfine splittings ofmagnitude similar to the estimated uncertainties in the as-sumed rotational constants. We crudely estimatedxaa'260 MHz, a value in betweenxaa and xzz of SCl2.The z principal axis of the quadrupole coupling tensor ofSCl2 is nearly parallel to the SCl bond,14 and the angle/(az) of ClSF was expected to lie between 0° and that ofSCl2.

Initial searches were carried out fora-type transitionsbecause their prediction was more accurate. They were rela-tively easily found in the expected frequency ranges, butwere rather weak, and required long microwave pulses to beseen. Though this was initially surprising to us, the structurein Fig. 1 gives a rationale. When the dipole moment is esti-

mated using bond moments from the dipole moments ofSF2 ~mb51.05 D3! and SCl2 ~mb50.3660.01 D1!, the com-ponents for the SF and SCl bonds along thea axis nearlycancel, while those along theb axis add. This rough methodleads to dipole moment componentsma'0.8310230 C m~0.24 D!, mb'2.8310230 C m ~0.84 D! for ClSF. This ra-tionale was confirmed when theb-type lines were found tobe much stronger than thea-type lines. In our frequencyrange the observed spectrum was dominated by strongb-type transitions ~mainly bQ121 and bR11! and muchweakera-type transitions (aR01).

In order to give an impression of the quality of the data,Fig. 2 compares the S/N ratios of one of the strongest andone of the weakest measured transitions. The left-hand sideof Fig. 2 shows a strongb-type transition of the parent spe-cies 35Cl32S19F, while the right-hand side shows a muchweakera-type transition of the species35Cl34S19F, whoseconcentration in natural isotopic abundance is lower by afactor of approximately 22. This figure presents the powerspectra obtained by fast Fourier transformation~FFT! of themeasured time-domain signals.

All transitions show hyperfine structures due to nuclearquadrupole coupling with the Cl nucleus~both 35Cl and37Cl have I53/2! and to spin–rotation coupling with the19F nucleus (I51/2), with the latter not always resolved.Since the hyperfine splittings caused by35Cl/37Cl are muchbigger than those caused by19F, the lines were assigned interms of the following, serial coupling scheme:J1ICl5F1 ;F11IF5F. ~Isotopomers with33S, which would have threenuclei with nonzero nuclear spin, were not observed.! Sincethe Cl hyperfine splitting is very large, the resulting compo-

FIG. 1. Geometry of ClSF in its principal axis system, drawn to scale usingthe r s coordinates obtained in this work. The size of the circles symbolizingthe atoms codes for the relative atomic masses of the parent isotopomer,35Cl32S19F.

10038 J. Preusser and M. C. L. Gerry: FT microwave spectrum of ClSF

J. Chem. Phys., Vol. 106, No. 24, 22 June 1997 This article is copyrighted as indicated in the article. Reuse of AIP content is subject to the terms at: http://scitation.aip.org/termsconditions. Downloaded to IP:

155.247.166.234 On: Sat, 22 Nov 2014 10:03:48

nents are well resolved in each case and theF1 assignmentdid not cause any problem even without having accuraterelative intensities of the different components of a rotationaltransition. However, this is not the case for the spin–rotationsplittings caused by19F. Some of the transitions were par-tially resolved, and others only showed shoulders indicatingthat there were several components underneath.

The 35Cl nuclear quadrupole splitting is illustrated inFig. 3, which gives an overview of theb-type rotational tran-sition 110←101 of the parent species with all its hyperfine

components due to35Cl, which spread over a region of ap-proximately 50 MHz. The19F spin–rotation splitting cannotbe seen at this graphical resolution; even the much largerDoppler splitting is hardly visible. The displayed spectrum isa composite of seven different spectra taken at different ex-citation frequencies and at different times. Therefore therelative intensities of the components only roughly reflect thetrue pattern. An example of the additional19F spin–rotationsplittings is given in Fig. 4. It presents two different35Clquadrupole components of the transition 110←101 of the par-ent species, one of which (F155/2←5/2) shows a partiallyresolved splitting while the other (F153/2←1/2) has only ashoulder.

All line positions were determined by directly fitting thetime-domain signals obtained by the experiments with theprogramDECAYFIT,15 in order to avoid inaccuracies causedby distortions in the power spectra.16 Using this technique,

FIG. 2. Illustration of the quality of the observed spectra~all signals appearas power spectra containing Doppler doublets!. The left-hand side shows thestrongest feature in the observed frequency range with the best S/N ratioachieved ~parent species,JKaKc5111←000 , F151/2←3/2, 19F spin–rotation splitting indicated by shoulder, 512 coadded experiments!. Theright-hand side shows one of the weakest lines observed~35Cl34S19F,JKaKc5101←000 , F155/2←3/2, 19F-spin–rotation splitting not resolved,3072 coadded experiments!. The figures have been scaled to equal peakheight to compare their S/N ratio.

FIG. 3. Composite power spectrum showing all35Cl quadrupole hyperfinecomponents of the transitionJKaKc5110←101 of the species

35Cl32S19F. Therelative intensities reflect only roughly the true intensity pattern, because thelines cannot be recorded under the same experimental conditions. The usualDoppler splitting lies within the graphical resolution; the19F spin–rotationsplitting is even smaller.

FIG. 4. Part of the power spectrum of35Cl32S19F showing two35Cl quadru-pole hyperfine components of the transition 110←101 close enough to beobservable within one scan.~256 coadded experiments, excitation frequency18 235.650 MHz.! The 19F spin–rotation splitting is partially resolved forthe F155/2←5/2 component while theF153/2←1/2 component has amuch smaller splitting and only shows a shoulder towards higher frequency.

TABLE I. Numbers of measured lines for three different isotopomers ofClSF in natural abundance.

Transition

35Cl32S19F 37Cl32S19F 35Cl34S19F

35Cla All b 37Cla All b 35Cla All b

101← 000 3 3 3 3 2 2212← 111 7 9 3 4202← 101 8 8 5 5211← 110 6 9 2 3110← 101 7 14 7 13 6 9211← 202 10 20 6 11312← 313 10 20 2 4413← 404 4 8111← 000 3 6 3 6 3 6404← 313 2 4

aNumber of different observed Cl nuclear quadrupole components.bTotal number of observed individual lines including19F spin–rotation.

10039J. Preusser and M. C. L. Gerry: FT microwave spectrum of ClSF

J. Chem. Phys., Vol. 106, No. 24, 22 June 1997 This article is copyrighted as indicated in the article. Reuse of AIP content is subject to the terms at: http://scitation.aip.org/termsconditions. Downloaded to IP:

155.247.166.234 On: Sat, 22 Nov 2014 10:03:48

TABLE II. Measured transitions of35Cl32S19F.

Transitionan

MHzno2nc

kHzTransitiona

n

MHzno2nc

kHz

101← 0003/2, 2← 3/2, 1 8 593.5107~10!b 0.45/2, 3← 3/2, 2 8 608.3509~10! 20.21/2, 1← 3/2, 2 8 620.2155~10! 0.4

212← 1115/2, 3← 3/2, 2 16 362.3337~30! 0.55/2, 2← 5/2, 2 16 364.9741~20! 21.35/2, 3← 5/2, 3 16 364.9904~20! 0.53/2, 2← 3/2, 2 16 371.0314~30! 20.83/2, 2← 1/2, 1 16 375.8113~30! 20.37/2, 3← 5/2, 2 16 377.1570~20! 20.77/2, 4← 5/2, 3 16 377.1715~20! 0.61/2, 1← 3/2, 2 16 383.2128~30! 20.91/2, 1← 1/2, 1 16 387.9960~30! 3.0

202← 1013/2, 2← 1/2, 1 17 166.2828~20! 20.55/2, 3← 5/2, 3 17 167.4193~20! 20.23/2, 2← 5/2, 3 17 178.1474~30! 0.21/2, 1← 1/2, 1 17 181.2991~20! 21.45/2, 3← 3/2, 2 17 182.2593~10! 21.07/2, 4← 5/2, 3 17 182.5112~10! 20.33/2, 1← 3/2, 1 17 192.9877~20! 2.31/2, 1← 3/2, 2 17 208.0052~30! 20.1

211← 1105/2, 3← 3/2, 2 18 036.6412~20! 1.23/2, 2← 3/2, 2 18 038.5316~30! 0.25/2, 2← 5/2, 2 18 048.8356~30! 21.95/2, 3← 5/2, 3 18 048.8518~30! 1.87/2, 3← 5/2, 2 18 051.4884~20! 20.47/2, 4← 5/2, 3 18 051.5001~20! 1.23/2, 2← 1/2, 1 18 060.4325~30! 0.73/2, 1← 1/2, 0 18 060.4537~50! 21.01/2, 1← 1/2, 1 18 063.1106~100! 6.1

110← 1011/2, 0← 1/2, 1 18 214.0463~20! 21.61/2, 1← 1/2, 1 18 214.0614~10! 0.35/2, 3← 5/2, 3 18 235.6162~10! 0.75/2, 2← 5/2, 2 18 235.6411~10! 21.13/2, 2← 1/2, 1 18 235.9607~20! 20.93/2, 1← 1/2, 0 18 235.9726~20! 2.01/2, 0← 3/2, 1 18 240.7511~20! 22.81/2, 1← 3/2, 2 18 240.7662~10! 0.33/2, 2← 5/2, 3 18 247.8241~10! 21.43/2, 1← 5/2, 2 18 247.8411~10! 2.15/2, 3← 3/2, 2 18 250.4575~10! 1.25/2, 2← 3/2, 1 18 250.4802~10! 21.23/2, 2← 3/2, 2 18 262.6661~10! 20.23/2, 1← 3/2, 1 18 262.6770~20! 21.2

404← 31311/2, 5← 9/2, 4 18 689.6075~30! 21.111/2, 6← 9/2, 5 18 689.6191~30! 0.49/2, 4← 7/2, 3 18 689.7882~30! 0.49/2, 5← 7/2, 4 18 689.7983~30! 0.9

211← 2023/2, 2← 1/2, 1 19 093.1920~20! 20.4

3/2, 1← 1/2, 0 19 093.2079~30! 1.01/2, 1← 1/2, 1 19 095.8650~20! 20.11/2, 0← 1/2, 1 19 095.8779~20! 0.85/2, 3← 7/2, 4 19 101.9544~10! 0.45/2, 2← 7/2, 3 19 101.9701~10! 20.87/2, 4← 7/2, 4 19 104.6032~10! 0.47/2, 3← 7/2, 3 19 104.6223~10! 0.15/2, 3← 3/2, 2 19 106.3185~10! 0.25/2, 2← 3/2, 1 19 106.3333~20! 20.33/2, 2← 3/2, 2 19 108.2088~10! 20.93/2, 1← 3/2, 1 19 108.2247~20! 1.51/2, 1← 3/2, 2 19 110.8829~10! 0.61/2, 0← 3/2, 1 19 110.8990~20! 0.75/2, 3← 5/2, 3 19 117.0461~10! 0.05/2, 2← 5/2, 2 19 117.0622~10! 0.23/2, 2← 5/2, 3 19 118.9369~10! 20.63/2, 1← 5/2, 2 19 118.9519~10! 0.27/2, 4← 5/2, 3 19 119.6958~10! 0.97/2, 3← 5/2, 2 19 119.7125~10! 20.8

312← 3035/2, 3← 3/2, 2 20 450.0196~20! 21.75/2, 2← 3/2, 1 20 450.0403~20! 3.57/2, 4← 9/2, 5 20 454.1952~20! 22.47/2, 3← 9/2, 4 20 454.2139~20! 0.23/2, 2← 3/2, 2 20 456.4597~20! 0.13/2, 1← 3/2, 1 20 456.4753~20! 20.69/2, 5← 9/2, 5 20 460.6292~20! 20.99/2, 4← 9/2, 4 20 460.6486~20! 1.67/2, 4← 5/2, 3 20 462.3902~30! 20.27/2, 3← 5/2, 2 20 462.4048~30! 20.75/2, 3← 5/2, 3 20 465.3878~30! 20.45/2, 2← 5/2, 2 20 465.4035~30! 0.67/2, 4← 7/2, 4 20 469.5580~30! 21.57/2, 3← 7/2, 3 20 469.5755~30! 0.63/2, 2← 5/2, 3 20 471.8256~30! 20.93/2, 1← 5/2, 2 20 471.8425~30! 0.55/2, 3← 7/2, 4 20 472.5572~30! 20.15/2, 2← 7/2, 3 20 472.5713~30! 21.19/2, 5← 7/2, 4 20 475.9919~30! 20.19/2, 4← 7/2, 3 20 476.0071~30! 21.0

413← 4045/2, 3← 5/2, 3 22 365.1265~30! 1.05/2, 2← 5/2, 2 22 365.1419~30! 0.211/2, 6← 11/2, 6 22 367.8445~30! 1.211/2, 5← 11/2, 5 22 367.8592~30! 20.67/2, 4← 7/2, 4 22 372.8801~40! 20.27/2, 3← 7/2, 3 22 372.8962~40! 0.69/2, 5← 9/2, 5 22 375.5984~40! 0.09/2, 4← 9/2, 4 22 375.6116~40! 22.4

111← 0001/2, 0← 3/2, 1 26 006.0841~20! 2.41/2, 1← 3/2, 2 26 006.0930~20! 0.05/2, 3← 3/2, 2 26 008.2151~10! 20.75/2, 2← 3/2, 1 26 008.2367~10! 0.73/2, 2← 3/2, 2 26 010.8720~20! 20.43/2, 1← 3/2, 1 26 010.8810~20! 20.4

aJKa8Kc8

8 ←JKa9Kc9

9 / F18 , F8←F19 , F9.bEstimated experimental uncertaintiess in the last digits are given in parentheses. All transitions were weighted by 1/s2 during the fitting procedures.

10040 J. Preusser and M. C. L. Gerry: FT microwave spectrum of ClSF

J. Chem. Phys., Vol. 106, No. 24, 22 June 1997 This article is copyrighted as indicated in the article. Reuse of AIP content is subject to the terms at: http://scitation.aip.org/termsconditions. Downloaded to IP:

155.247.166.234 On: Sat, 22 Nov 2014 10:03:48

TABLE III. Measured transitions of37Cl32S19F.

Transitionan

MHz

no2nc

kHz Transitionan

MHz

no2nc

kHz

101← 000 5/2, 3← 3/2, 2 18 277.9219~10! 1.03/2, 2← 3/2, 2 8 362.7693~10!b 0.2 5/2, 2← 3/2, 1 18 277.9447~10! 21.55/2, 3← 3/2, 2 8 374.5455~10! 20.9 5/2, 2← 3/2, 2 18 287.5339~20! 0.31/2, 1← 3/2, 2 8 383.9605~10! 0.6 5/2, 1← 3/2, 1 18 287.5444~30! 21.3

212← 111 211← 2025/2, 3← 3/2, 2 15 940.2225~30! 20.5 3/2, 2← 1/2, 1 19 080.6710~20! 20.13/2, 2← 3/2, 2 15 947.0743~30! 23.3 3/2, 1← 1/2, 0 19 080.6798~40! 26.57/2, 3← 5/2, 2 15 951.9850~20! 0.4 1/2, 1← 1/2, 1 19 082.8580~20! 1.97/2, 4← 5/2, 3 15 951.9997~20! 1.0 5/2, 3← 7/2, 4 19 087.5991~20! 21.5202← 101 5/2, 2← 7/2, 3 19 087.6213~20! 3.03/2, 2← 1/2, 1 16 705.9647~30! 22.1 7/2, 4← 7/2, 4 19 089.7701~10! 20.55/2, 3← 5/2, 3 16 706.8679~30! 1.3 7/2, 3← 7/2, 3 19 089.7906~10! 20.15/2, 3← 3/2, 2 16 718.6426~50! 21.3 3/2, 2← 3/2, 2 19 092.5847~20! 21.27/2, 4← 5/2, 3 16 718.8177~20! 0.7 3/2, 1← 3/2, 1 19 092.6041~30! 4.14/3, 2← 3/2, 2 16 727.1576~30! 0.1 5/2, 3← 5/2, 3 19 099.5500~10! 21.0211← 110 5/2, 2← 5/2, 2 19 099.5686~10! 1.15/2, 3← 3/2, 2 17 530.6618~30! 0.6 312← 3037/2, 3← 5/2, 2 17 542.4301~20! 23.4 9/2, 5← 9/2, 5 20 372.7213~20! 20.67/2, 4← 5/2, 3 17 542.4471~20! 3.2 9/2, 4← 9/2, 4 20 372.7390~20! 20.8110← 101 7/2, 4← 7/2, 4 20 379.7165~20! 21.01/2, 0← 1/2, 1 18 249.0622~20! 21.0 7/2, 3← 7/2, 3 20 379.7361~20! 2.21/2, 1← 1/2, 1 18 249.0764~10! 0.0 111← 0005/2, 3← 5/2, 3 18 266.1446~10! 0.9 1/2, 0← 3/2, 1 25 844.8381~30! 24.75/2, 2← 5/2, 2 18 266.1709~10! 0.0 1/2, 1← 3/2, 2 25 844.8542~10! 0.53/2, 2← 1/2, 1 18 266.3513~40! 8.5 5/2, 3← 3/2, 2 25 846.5903~10! 20.71/2, 0← 3/2, 1 18 270.2573~20! 1.8 5/2, 2← 3/2, 1 25 846.6112~10! 0.61/2, 1← 3/2, 2 18 270.2666~10! 20.6 3/2, 2← 3/2, 2 25 848.7655~10! 0.13/2, 2← 5/2, 3 18 275.7567~10! 0.4 3/2, 1← 3/2, 1 25 848.7753~30! 1.23/2, 1← 5/2, 2 18 275.7692~10! 21.1

aJKa8Kc8

8 ←JKa9Kc9

9 /F18 , F8←F19 , F9.bEstimated experimental uncertaintiess in the last digits are given in parentheses. All transitions were weightedby 1/s2 during the fitting procedures.

TABLE IV. Measured transitions of35Cl34S19F.

Transitionan

MHz

no2nc

kHz Transitionan

MHz

no2nc

kHz

101← 000 111← 0003/2, 2← 3/2, 2 8 529.4108~20!b 20.7 1/2, 0← 3/2, 1 25 265.0168~30! 20.35/2, 3← 3/2, 2 8 544.3973~20! 0.7 1/2, 1← 3/2, 2 25 265.0235~20! 23.7110← 101 5/2, 3← 3/2, 2 25 267.2690~10! 20.15/2, 3← 5/2, 3 17 572.7651~20! 20.3 5/2, 2← 3/2, 1 25 267.2883~10! 1.05/2, 2← 5/2, 2 17 562.7918~20! 1.6 3/2, 2← 3/2, 2 25 270.0739~20! 0.93/2, 2← 1/2, 1 17 573.0267~40! 6.7 3/2, 1← 3/2, 1 25 270.0797~30! 21.41/2, 1← 3/2, 2 17 578.1113~40! 24.43/2, 2← 5/2, 3 17 584.9974~20! 22.03/2, 1← 5/2, 2 17 585.0136~20! 1.75/2, 3← 3/2, 2 17 587.7510~10! 0.45/2, 2← 3/2, 1 17 587.7727~10! 21.03/2, 2← 3/2, 2 17 599.9887~40! 4.2

aJKa8Kc8

8 ←JKa9Kc9

9 / F18 , F8←F19 , F9.bEstimated experimental uncertaintiess in the last digits are given in parentheses. All transitions were weightedby 1/s2 during the fitting procedures.

10041J. Preusser and M. C. L. Gerry: FT microwave spectrum of ClSF

J. Chem. Phys., Vol. 106, No. 24, 22 June 1997 This article is copyrighted as indicated in the article. Reuse of AIP content is subject to the terms at: http://scitation.aip.org/termsconditions. Downloaded to IP:

155.247.166.234 On: Sat, 22 Nov 2014 10:03:48

we were able to determine the frequencies of at least two ofthe spin–rotation components for the partially resolved quad-rupole components and for most of those which showed onlyshoulders. The intensity patterns within such a spin–rotationmultiplet were quite accurate, since the different lines wereonly a few kHz apart. This information could be successfullyused to assign theF quantum numbers unambiguously, aidedby simulations of the patterns using the programSPCATwrit-ten by Pickett,17 although none of the spin–rotation patternswere fully resolved.

Table I summarizes the numbers of lines which wereobserved for the three species35Cl32S19F, 37Cl32S19F, and35Cl34S19F. For each species, Table I gives the number of~fully resolved! 35Cl quadrupole hyperfine components andthe total number of hyperfine components including the19Fspin–rotation splitting~not fully resolved! obtained for agiven rotational transition. Missing components were eithertoo weak or overlapped.

All measured frequencies together with their estimatedexperimental errors and the differences from the calculatedfrequencies resulting from fits with the program package ofPickett17 are given in Tables II–IV. The experimental errorswere estimated using the S/N ratio and the quality of the timedomain fits in the case of small splittings or shoulders.

In order to obtain molecular constants the data were fit-ted to Watson’s Hamiltonian in theA reduction using Pick-ett’s least-squares programSPFIT.17 In a first stage, the19Fspin–rotation splittings were ignored and a rough intensity

weighted average frequency for those transitions whichshowed splittings was used instead. This resulted in prelimi-nary rotational constants, some quartic centrifugal distortionconstants, and35Cl nuclear quadrupole coupling constantsfor the parent isotopomer.

Since there were not enough data, the quartic centrifugaldistortion constantsDK anddK could not be determined. Wetherefore fixed these two constants at values obtained usingthe force constants and fundamental vibrational frequenciesof Willner5 and a structure derived from the preliminary ro-tational constants. This was done with the programNORCOR

written by Christen.18 The resulting values forDK anddK arenot supposed to be very accurate, since the vibrational fre-quencies in the gas phase will not be the same as those mea-

TABLE V. Rotational, quartic centrifugal distortion and nuclear quadrupole and spin–rotation hyperfine cou-pling constants of the observed ClSF isotopomers.a

35Cl32S19F 37Cl32S19F 35Cl34S19F

A/MHz 22 125.045 17~57!b 22 058.897 82~75! 21 423.155 28~127!B/MHz 4 721.528 56~43! 4 583.909 20~63! 4 696.573 22~194!C/MHz 3 883.859 263~187! 3 788.287 51~40! 3 844.831 09~130!DJ /kHz 2.288 16~160! 2.746 ~57! 2.88 16c

DJK /kHz 215.507 ~124! 214.620 ~227! 215.507c

DK /kHz 200.0d 200.0d 200.0d

dJ /kHz 0.736 7 ~56! 0.639 5 ~194! 0.736 7c

dK /kHz 12.0d 12.0d 12.0d

xaa(Cl!/MHz 259.349 49~106! 247.096 12~149! 259.926 7 ~49!x2(Cl!/MHz 238.094 7 ~23! 229.698 4 ~30! 237.490 3 ~92!xab(Cl!/MHz 637.637 ~150! 629.06 ~42! 637.57 ~47!xbb(Cl!/MHz

e 10.627 4 ~26! 8.698 9 ~35! 11.218 2 ~106!xcc(Cl!/MHz

f 48.722 09~126! 38.397 24~169! 48.708 5 ~52!Caa(Cl!/kHz 3.55 ~42! 3.08 ~41! 3.55c

Cbb(Cl!/kHz 0.631 ~188! 0.5g 0.631c

Ccc(Cl!/kHz 2.170 ~191! 1.891 ~285! 2.17c

Caa(F!/kHz 239.19 ~117! 239.07 ~122! 235.78 ~154!Cbb(F!/kHz 20.58 ~73! 20.58c 20.58c

Ccc(F!/kHz 5.33 ~60! 6.33 ~83! 5.51 ~177!

aConstants were determined by using theI r representation.bEstimated~single! uncertainties in the last digits are given in parentheses. Values without uncertainties werefixed, see the text.cFixed to the corresponding values of the parent species.dFixed to estimated values resulting from a normal coordinate analysis using data from Ref. 5.eCalculated according toxbb5xcc1x2 .fCalculated according toxcc521/2(xaa1x2).gFixed to the value of the parent species corrected by the ratio of the nuclear magnetic momentsm(35Cl)/m(37Cl)'1.2 given in Ref. 19.

TABLE VI. Structural parametersa of ClSF.

r ~SF!/pm r ~SCl!/pm /~ClSF!/deg

r 0 161.032 ~82! 199.439 ~81! 100.740 ~32!rDP 160.616 ~97! 199.429 ~53! 100.742 ~57!r s 160.653 ~162! 199.437 ~65! 100.732 ~81!r z 160.998 ~44! 199.89 ~15! 100.661 ~16!r e

b 160.604 199.401 100.661ab initioc 161.6 202.8 101.0

aUncertainties given reflect those produced in the least-squares fits; absoluteuncertainties are probably somewhat larger.bEstimatedr e structure derived fromr z , see the text.cFrom Ref. 6.

10042 J. Preusser and M. C. L. Gerry: FT microwave spectrum of ClSF

J. Chem. Phys., Vol. 106, No. 24, 22 June 1997 This article is copyrighted as indicated in the article. Reuse of AIP content is subject to the terms at: http://scitation.aip.org/termsconditions. Downloaded to IP:

155.247.166.234 On: Sat, 22 Nov 2014 10:03:48

sured by Willner5 in rare gas matrices, and no account wastaken of anharmonicity. Nevertheless, the estimated valuesfor DK anddK are reasonable compared to the correspondingconstants of SF2 and SCl2. Using these values is definitelybetter than being forced to fix these two constants to zero; anerror in the centrifugal distortion constants would be other-wise transferred into~wrong! rotational constants by the fit-ting procedure and would therefore affect the structure deter-mination, which was one of the goals of this work.

In the course of these early fits it was also found neces-sary to include the off-diagonal matrix elementxab of thequadrupole coupling tensor to fit the35Cl/37Cl quadrupolesplittings. This parameter has an especially large effect ontransitions involving interacting energy levels with the ap-propriate symmetry~in this case;DF50; DJ50, 61, 62;KaKc5ee↔oe or eo↔oo!, if the energy separation be-tween these levels is small. In ClSF this is the case for thelevels 202 and 110, whose term values are separated by only1058.3 MHz (0.0353 cm21) in the case of the parent species.

The second stage of the fits included the19F spin–rotation coupling. In this case, all directly measured line po-sitions were used. In the case of overlapping lines, only thestrongest component was used, while weaker ones known tolie underneath were not included. The correctF assignmentcould be achieved by carefully interpreting the intensity pat-terns of some of the multiplets. The assignments obtainedfrom those unambiguous patterns were used to assign thosemultiplets where the intensity pattern did not provide clearinformation. The results were not completely satisfactory be-fore the additional inclusion of35Cl/37Cl spin–rotation cou-pling constants. Although these could not be determined withhigh accuracy, their inclusion helped to achieve a fit with,according to the quality of the data, reasonable standard de-viation and appropriate observed minus calculated frequencydifferences. The inclusion of19F–35Cl spin–spin couplingconstants fixed to values estimated from the geometry didnot shift the remaining constants outside their uncertaintyranges; spin–spin constants were thus omitted in the finalfits.

The resulting molecular constants for all three observedisotopomers are presented in Table V. In the case of theparent species only the constantsDK anddK had to be fixedto estimated values~see above!. The constantCbb(F) couldnot be determined but was not fixed in the fit to get anestimate of its value. It turned out to be approximately zerowhich is confirmed by the fact that fixing it to zero does notchange the quality of the fit, and its uncertainty is compa-rable to those of the other19F spin–rotation constants. Thevalue obtained was used for the other isotopomers as a fixedparameter instead of zero. For the isotopomer37Cl32S19F weadditionally had to fix the constantsCbb(Cl) to the value ofthe species35Cl32S19F scaled by the ratio of the nuclear mag-netic momentsm(35Cl)/m(37Cl), which is approximately1.2.19 Since the number of available line positions of35Cl34S19F was much smaller~only the transitions involvinglevels withJ50,1 could be observed!, we fixed all centrifu-gal distortion and all35Cl spin–rotation coupling constants tothe corresponding values of the parent species.

Since the constantsxaa , xbb , andxcc are not linearlyindependent, we fittedxaa and x25xbb2xcc from whichthe values forxbb andxcc given in Table V were calculatedfrom xcc521/2(xaa1x2) andxbb5xcc1x2 .

IV. DISCUSSION AND CONCLUSIONS

A. Structure determination

The rotational constants given in Table V were used tocalculate the geometrical parameters.r 0-type andr s-type

20

structures were calculated using Rudolph’s programsRU111J21 and RU238J,22,23 respectively. These least-squaresprograms can be used to fit the structural parameters of amolecule to either the rotational constants,Bg ~with g5a,b,c!, to the moments of inertia,I g, to the planar mo-mentsPg, or to the differences of these quantities betweenisotopomers.

For r 0-type structures we also used two fitting methodswhich partially account for vibrational effects. For bothmethods these effects are described by

I 0g5I e

g1eg, ~1!

where theeg are the vibration–rotation interaction param-eters. The first fitting method assumes that theeg are isoto-pically independent and results in the structures denoted byr I ,e and r P,e . These two structures are identical when thesame input data are used in the fit; the different designationssignify which type of data~I—moments of inertia orP—planar moments! have been used. The same resultingstructure can also be calculated by the second fitting method,which accounts for the vibrational effects by fitting to theisotopic differences inI g or Pg, thus canceling the vibra-tional effects to the extent that they are isotopically invariant.The resulting structures are designated byrDI or rDP , re-spectively. The structuresr I ,e /r P,e andrDI /rDP are identicalwhen the same input data are used, butrDI /rDP are moresuitable for correcting for Costain’s error21,24 ~uncertaintiesin the coordinates of substituted atoms are inversely propor-tional to their absolute magnitudes!.

In the case of ther 0 andrDP structures, we followed therecommendation of Rudolph to fit to the principal planarmomentsPa andPb and omitPc, because of the planarity ofClSF.25 Table VI presents the results. The corresponding val-ues forr I ,e /r P,e , andrDI did not differ from rDP when thesame input was used and are therefore omitted. For therDP

structure we additionally accounted for Costain’s error. In allcalculations the data were weighted according to the inversesquares of their uncertainties as given in Table V.

An r s-type structure using35Cl32S19F as the basis mol-ecule was also obtained. The fit included the nontrivial first-and second-moment conditions, which give more accuratecoordinates for atoms close to an inertial axis, or for whichno isotopic data are available,21 in this case F. In the presentfits the data were weighted in the same way as for ther 0-type structures. The resulting geometry is also given inTable VI.

In order to evaluate the ground-state average structure,r z , a harmonic force field calculation~as described in Sec.

10043J. Preusser and M. C. L. Gerry: FT microwave spectrum of ClSF

J. Chem. Phys., Vol. 106, No. 24, 22 June 1997 This article is copyrighted as indicated in the article. Reuse of AIP content is subject to the terms at: http://scitation.aip.org/termsconditions. Downloaded to IP:

155.247.166.234 On: Sat, 22 Nov 2014 10:03:48

IV B ! had to be carried out to obtain the harmonic contribu-tions to thea constants. These were subtracted off the ex-perimental rotational constantsB0

g ~see Table V!. The result-ing constantsBz

g were used in fits of the structural parametersusing Typke’s programMWSTR.26 Isotopic variations in thebond lengths were accounted for using27

dr53/2ad^u2&2dK, ~2!

where^u2& andK are the zero-point mean-square amplitudeof a given bond and its perpendicular amplitude~both ob-tained from the force field!, anda is the Morse anharmonic-ity parameter for the bond, approximated from the corre-sponding diatomics.28 The values 0.016 46 pm21 for SCl

~derived from Ref. 29! and 0.018 92 pm21 for SF ~derivedfrom Ref. 30! were used. The resultingr z parameters aregiven in Table VI. Again the input data were weighted ac-cording to their uncertainties.

The r z structure was finally used to estimate the equilib-rium bond lengths according to27

r e5r z23/2a^u2&1K, ~3!

while changes in the bond angle were neglected. The result-ing estimate for ther e structure is presented in Table VI andcompared to the calculated structure of Gutsev and Ziegler.6

TABLE VII. Quadratic force constants and potential energy distribution of the general valence force field.

Force constantsa (100 N m21)f SCl f SF fClSF f SCl/SF f SCl/ClSF f SF/ClSF

This work 2.937~1! 4.28 ~3! 1.1519 ~1! 0.700 ~2! 0.0469 ~2! 0.103 ~8!Ref. 5 2.90 4.30 1.15 0.35b 0.04 0.10b

f SF f FSF f SF/SF f SF/FSF

SF2 Ref. 45 4.72 1.28 0.37 0.09

f SCl fClSCl f SCl/SCl f SCl/ClSCl

SCl2 Ref. 46 2.77 1.032 0.34 0.17

Potential energy distributionc

f SCl f SF fClSF f SCl/SF f SCl/ClSF f SF/ClSF

n1 0.954 0.033n2 0.975 0.088 0.058 20.116n3 0.059 0.926

aDeformation constant normalized to 100 pm bond length. The given uncertainties represent solely the standarderrors obtained in the fit, and reflect the somewhat arbitrary weighting scheme used. The values should berevised when gas phase IR spectra become available. See the text for further details.bFixed in Ref. 5.cFor 35Cl32S19F; only contributions>0.03 are given.

TABLE VIII. Comparison of experimental and force field calculated parameters.

35Cl32S19F 37Cl32S19F 35Cl34S19F

Obs. Calc. Obs. Calc. Obs. Calc.

Wave numbersa

n1 /cm21 781.3 781.8 781.1 781.4 772.7 773.2

n2 /cm21 552.4 544.8 546.1 538.8 544.0 535.7

n3 /cm21 277.0 278.3 274.5 276.0 277.1

Centrifugal distortion constantsDJ /kHz 2.8816 2.8820 2.746 2.715 2.8046DJK /kHz 215.507 215.493 214.620 214.725 213.692DK /kHz

b 200.0 212.7 200.0 209.6 196.6dJ /kHz 0.7367 0.7364 0.6395 0.6793 0.7286dK /kHz

b 12.0 12.1 12.0 11.7 11.8

Inertial defectsD0 /(uÅ

2)c 0.2438 0.2422 0.2446 0.2430 0.2475 0.2460

aAll experimental wave numbers in solid Ne from Ref. 5. These wave numbers in solid Ar differ by as much as'8 cm21.b‘‘Experimental’’ constantsDK anddK had to be estimated because of insufficient data; see the text.c1u Å251.660 54310247 kg m2 ~Ref. 19!.

10044 J. Preusser and M. C. L. Gerry: FT microwave spectrum of ClSF

J. Chem. Phys., Vol. 106, No. 24, 22 June 1997 This article is copyrighted as indicated in the article. Reuse of AIP content is subject to the terms at: http://scitation.aip.org/termsconditions. Downloaded to IP:

155.247.166.234 On: Sat, 22 Nov 2014 10:03:48

The uncertainties of all derived structures presented inTable VI are those directly from the least-squares fits, andare probably too small in absolute terms, especially for ther 0 and r s structures, where the degree of vibrational contri-butions to the rotational constants is unknown. It is interest-ing that therDP and r s geometries are in excellent agree-ment, and their bond lengths also agree with those of theapproximater e geometry, which was obtained by a ratherdifferent route. Figure 1 summarizes the geometry of ClSFby showing the molecule in its principal axis system usingthe r s coordinates. The sizes of the circles symbolizing theatoms code for the relative atomic masses of the parent iso-topomer,35Cl32S19F.

The premise that the geometry of ClSF is a hybrid ofthose of SCl2 and SF2 is roughly confirmed by the presentresults. Even so, the SCl bond is slightly shorter in ClSF thanin SCl2 @r 0(SCl)5199.4 vs 201.4 pm,2 respectively#. Corre-spondingly, the SF bond in ClSF is slightly longer than inSF2 @r 0(SF)5161.0 vs 158.9 pm,3 respectively#. The bondangle is very close to the mean. In fact, the SCl bond lengthin ClSF is close to the one in sulfuryl chloride fluoride,SO2ClF @r 0(SCl!5198.5 pm31#, while the same bond lengthin SO2Cl2 @r g(SCl!5201.2 pm32# is close to the one inSCl2. In both pairs SCl2 /ClSF and SO2Cl2 /SO2ClF the SClbond length is shortened by approximately 1% by the substi-tution of one Cl by an F atom.

B. Harmonic force field

The general valence force field~GVFF! given byWillner5 and which had been used for the estimation of theundeterminable centrifugal distortion constantsDK and dK~see above! was refined by including the now available ex-perimental centrifugal distortion constants. This was donewith the programNCA written by Christen,18 which had alsobeen used by Willner. The program uses a least-squares pro-cedure to fit force constants to experimental data such asvibrational wave numbers, centrifugal distortion constants,and others, and is based on Gwinn’s method,33 avoiding theneed of setting up internal symmetry coordinates. The resultsof these refinement calculations were also used for the deter-mination of the r z structure and the estimation of ther estructure~see Sec. IV A!.

In the fitting procedures used to obtain the force con-stants we used the fundamental wave numbers given in Ref.5 and the newly determined centrifugal distortion constantsgiven in Table V. The data were weighted according theinverse squares of their experimental errors with some ex-ceptions. The centrifugal distortion constantsDK and dK ,

which could not be determined from the present experimen-tal data, were given very large error limits, which effectivelyheld them fixed and removed them from the fit. All the cen-trifugal distortion constants of the species35Cl34S19F weresimilarly removed from the fit. The error limits of the fun-damental wave numbers were set to values between 1 and2 cm21, although the actual errors are probably much larger,since these data were obtained in solid Ne and Ar matricesand are therefore not identical to gas phase wavenumbers,which are not yet available. One has to keep in mind that thewavenumbers differ by up to 8 cm21 between measurementsin Ne and in Ar matrices. Nevertheless, we chose the errorlimits stated above, because we think they are more appro-priate to describe therelative errors of those data. Anotherpoint is the known anharmonic resonance between 2n3 andn2 . The n2 wave numbers given by Willner had been onlyapproximately corrected for this resonance. They were there-fore given uncertainties twice as large as those of the otherwavenumbers in the present force field calculations.

Willner had to fix the two constantsf SCl/SF andfSF/ClSF, but with the aid of the new data it was possible to fitall six harmonic force constants. The results are given inTable VII, which also gives corresponding values for SF2

and SCl2 for comparison as well as the resulting potentialenergy distribution for the parent isotopomer,35Cl32S19F. Allderived force constants are in good agreement with the pre-vious values except for the constantf SCl/SF, which differsfrom the previous value by a factor of 2. This is one of theconstants which had been fixed earlier. We also tried to fixthis constant~and combinations with the constantf SF/ClSF! tothe previous values, but the resulting fits did not reproducethe centrifugal distortion constants with the same quality andalso produced larger sums of squared errors.

Table VIII compares the experimental values of the pa-rameters with the values resulting from the force field calcu-

TABLE IX. Principal chlorine quadrupole coupling constants.

35Cl32S19F 37Cl32S19F 35Cl34S19F

xzz(Cl!/MHz 275.749 ~172! 259.48 ~46! 276.09 ~52!xxx(Cl!/MHz 27.027 ~172! 21.08 ~46! 27.38 ~52!xyy(Cl!/MHz

a 48.722 09~126! 38.397 24~169! 48.708 5 ~52!uza /deg 223.54 ~21! 223.08 ~72! 223.28 ~64!

axyy(Cl)5xcc(Cl) because of the planarity of ClSF.

TABLE X. Comparison of the19F spin–rotation coupling constants andshielding components of ClSF and SF2.

a

ClSF SF2

Caa /kHz 239.19 ~117! 211.66 ~270!Cbb /kHz 20.58 ~73! 25.88 ~296!Ccc /kHz 5.33 ~60! 13.49 ~150!Caanuc/kHz 212.36 29.42

Cbbnuc/kHz 23.49 27.06

Cccnuc/kHz 25.04 27.64

Caael /kHz 226.83 ~117! 22.24 ~270!

Cbbel /kHz 2.91 ~73! 1.18 ~296!

Cccel /kHz 10.37 ~60! 21.13 ~150!

saap /ppm 211.8 ~92! 15 ~19!

sbbp /ppm 2107 ~27! 222 ~56!

sccp /ppm 2466 ~27! 2539 ~38!

saad /ppm 569 ~5! 541 ~5!

sbbd /ppm 602 ~5! 606 ~5!

sccd /ppm 693 ~5! 655 ~5!

saa /ppm 781 ~11! 556 ~19!sbb /ppm 495 ~28! 584 ~56!scc /ppm 227 ~28! 116 ~38!savg/ppm 501 ~40! 419 ~71!

aValues taken from Ref. 8.

10045J. Preusser and M. C. L. Gerry: FT microwave spectrum of ClSF

J. Chem. Phys., Vol. 106, No. 24, 22 June 1997 This article is copyrighted as indicated in the article. Reuse of AIP content is subject to the terms at: http://scitation.aip.org/termsconditions. Downloaded to IP:

155.247.166.234 On: Sat, 22 Nov 2014 10:03:48

lations. All wave numbers agree quite well except that ofn2 which differs by about 8 cm

21. However, the experimen-tal values for this parameter vary by just about this muchbetween the different rare gas matrices,5 so the agreement isstill good. This discrepancy is mostly attributed to the verydifferent value of the constantf SCl/SF obtained in this work~see Table VII! and can only be resolved when gas phase IRspectra become available. The agreement of experimentaland calculated centrifugal distortion constants is excellentand finally justifies the values assumed forDK anddK in thedetermination of the molecular constants.

The force field was also used to estimate the inertialdefects. This was done using the harmonic contributions tothe inertial moments which were required for the calculationof the r z geometry described above. The results are also inTable VIII. The excellent agreement shown there betweenthe observed and calculated values, including the isotopicvariations, provides further confirmation of the correctnessof the force field.

C. Chlorine nuclear quadrupole hyperfine constants

Precise values for the diagonal35Cl/37Cl nuclear quadru-pole coupling constants as indicated in Table V were ob-tained. The ratio xcc(

35Cl32S19F)/xcc(37Cl32S19F) is

1.268 896~65!, in excellent agreement with the ratio of thequadrupole momentsQ(35Cl)/Q(37Cl)51.268 877 3(15).34

Since we were able to determinexab , the completequadrupole coupling tensor was available for both35Cl and37Cl for all three observed isotopomers of ClSF. This al-lowed the straightforward determination of the principalquadrupole coupling constants for these nuclei without fur-ther assumptions. They axis of the principal quadrupole cou-pling tensor is identical to thec axis of the principal inertialsystem of the molecule because of theCs symmetry. Thisreduces the diagonalization of the quadrupole coupling ten-sor to the following three equations:

uza51/2 arctanS 2xab

xaa2xbbD , ~4!

xzz5xaa cos

2 uza2xbb sin2 uza

cos2 uza2sin2 uza, ~5!

xxx5xbb cos

2 uza2xaa sin2 uza

cos2 uza2sin2 uza, ~6!

whereuza is the angle between thez axis of the principalquadrupole coupling tensor and the inertiala axis. The re-sulting elements of the principal quadrupole coupling tensorand its orientation in the principal inertial system are givenin Table IX. For ther s structure~see above!, the angle of theSCl bond to thea axis is 224.06°. This means that theprincipal quadrupolar axis system is only very slightly tiltedby an angle between 0.5° and 1.0° with respect to the SClbond toward the center of gravity of the molecule. Althoughthe error ranges for theuza values~obtained through errorpropagation and given in Table IX! are relatively large, theydo not allow exact parallelism of thez axis and the SCl bond.The deviations from parallel are in the same direction for all

three isotopomers and are significant, but very small. Similarresults have been found for SCl2 ~Ref. 14! and SO2ClF.

31

In order to estimate the electronic character of the SClbond, we used the equations given in Ref. 35 and the quan-tities eQqn10(

35Cl!5109.74 MHz and eQqn10(37Cl!

586.51 MHz36 to calculate the ionic character of the sigmabond,i s , the backdonation from the out-of-plane 3py orbitalon Cl,pc , and the total ionic character of the bond,i c . Theresulting values of these quantities are 37.5%, 13.2%, and50.7%, respectively, averaged over all three isotopomers.The slight tilt between the SCl bond and thez axis of thequadrupolar tensor has been neglected for this purpose. Thetotal ionic character for a SCl bond in SCl2 calculated by thesame method is 41.8%~x values taken from Ref. 14!. Thisincrease of ionic bond character by substitution of one Clatom of SCl2 by an F atom can be qualitatively understoodby the additional electron withdrawing effect of the F atomaround the S nucleus compared to a second attached Cl atom.It is also consistent with the shorter SCl bond length in ClSFcompared to SCl2 ~see above!.

D. Fluorine spin–rotation hyperfine constants

The 19F spin–rotation constants~as given in Table V!are rather unusual, becausexaa and xbb are negative. Thishas only been found before for the interhalogen compoundsClF,37–39BrF, IF,12 and most recently for SF2.

8 In particular,xaa of ClSF is strongly negative, andxbb is essentially zero.The constants were used to estimate the components of the19F nuclear shielding tensor, using the methods describedearlier.40,41,12,8First of all, the nuclear contributions to thespin–rotation constants,Cgg

nuc, were evaluated from the de-rived geometry, and were subtracted from the experimentalvalues to produce the electronic contributions,Cgg

el . Theelectronic contributions are in turn directly proportional tothe paramagnetic19F shieldings,sgg

p , and were evaluatedusing Eq. ~6! of Ref. 8. The diamagnetic19F shieldings,sggd , were estimated fromCgg

nuc using Eq.~8! of Ref. 8 andvalues for the free-atom diamagnetic susceptibility of F fromRef. 42 and the charge distributions on S and Cl from Ref.41. Finally the componentssgg of the complete tensor wereevaluated assgg5sgg

p 1sggd . The average,savg51/3(saa

1sbb1scc), is the shielding normally obtained in typicalNMR experiments.

The results of these calculations are given in Table X, incomparison with the corresponding values for SF2. It is en-couraging, in particular, that there is reasonable agreementbetween the out-of-plane paramagnetic components,scc

p , forthe two molecules, as well as between the values ofsavg.Discrepancies between the two molecules for the remainingconstants are largely due to different relative directions ofthe SF bond in their respective inertial axis systems.

For SF2, the anomalous, negative,19F spin–rotation con-

stantsxaa andxbb , and their corresponding near-zero para-magnetic shieldingssaa

p and sbbp , were accounted for in

terms of the molecular electronic structure.8 In particular, itwas found that the highest occupied molecular orbital ofSF2, which is an out-of-planep* antibonding orbital located

10046 J. Preusser and M. C. L. Gerry: FT microwave spectrum of ClSF

J. Chem. Phys., Vol. 106, No. 24, 22 June 1997 This article is copyrighted as indicated in the article. Reuse of AIP content is subject to the terms at: http://scitation.aip.org/termsconditions. Downloaded to IP:

155.247.166.234 On: Sat, 22 Nov 2014 10:03:48

largely on S, was very near in energy~term value difference'18 000 cm2143! to the lowest unoccupied molecular or-bital, an in-planes* orbital, also largely located on S. Theanomalous values were due to second-order contributions in-volving these orbitals.

Given that the geometry of ClSF is essentially a hybridof those of SF2 and SCl2, it was highly likely that its anoma-lous Caa andCbb should have a similar origin. A detailedrationale requires knowledge of the wave functions of themolecular orbitals, and of the electronic spectrum. Sincethese are unavailable, a comparison was made between ClSFand SF2 in the following way. With the assumption that theSF bond is a principal axis of the19F shielding tensor, theprincipal valuesszz

p andsxxp of the paramagnetic contribu-

tions for ClSF were evaluated using

saap 5szz

p cos2 qza1sxxp sin2 qza , ~7!

sbbp 5szz

p sin2 qza1sxxp cos2 qza , ~8!

whereqza is the angle between thez axis of the shieldingtensor and thea inertial axis. The results wereszz

p

52405 ppm andsxxp 5510 ppm. When these were assumed

also to be the principal values in SF2, and transformed to itsinertial axes, the resulting values weresaa

p 5213 ppm andsbbp 5118 ppm. Given the approximations involved, and the

fact that both experimental values for SF2, though small,were indeterminable, the agreement is satisfactory. The ori-gin of the anomalous spin–rotation constants is the same forboth ClSF and SF2. It is interesting that the energy gap lead-ing to the anomaly in SF2, as shown by electronicspectroscopy43 is in the visible range of the spectrum. SCl2 isred, and has an absorption nearlmax5380 nm extending wellinto the visible region.44 Simply by analogy, with SF2 andSCl2, ClSF can reasonably be expected to show an electronictransition in the visible or near ultraviolet region of the spec-trum. The spin–rotation constants have provided strong evi-dence that this is indeed the case.

ACKNOWLEDGMENTS

J.P. wants to thank all members of the group for theirkind help at the beginning of the experiments and for pro-viding an excellent working atmosphere which he enjoyedvery much during his stay in Vancouver. We acknowledgegratefully the financial support of the Natural Sciences andEngineering Research Council of Canada.

1J. T. Murray, W. A. Little, Jr., Q. Williams, and T. L. Weatherly, J. Chem.Phys.65, 985 ~1976!.

2R. W. Davis and M. C. L. Gerry, J. Mol. Spectrosc.65, 455 ~1977!.3D. R. Johnson and F. X. Powell, Science164, 950 ~1969!.4Y. Endo, S. Saito, E. Hirota, and T. Chikaraishi, J. Mol. Spectrosc.77,222 ~1979!.

5H. Willner, Z. Naturforsch.39b, 314 ~1984!.6G. L. Gutsev and T. Ziegler, Inorg. Chem.31, 1909~1992!.7F. Seel, Advan. Inorg. Radiochem.16, 297 ~1974!.8B. Gatehouse, H. S. P. Mu¨ller, and M. C. L. Gerry, J. Chem. Phys.106,6916 ~1997!.

9T. J. Balle and W. H. Flygare, Rev. Sci. Instrum.52, 33 ~1981!.10C. Styger and M. C. L. Gerry, J. Mol. Spectrosc.158, 328 ~1993!.11C. Styger, B. Gatehouse, N. Heineking, W. Ja¨ger, and M. C. L. Gerry, J.Chem. Soc. Faraday Trans.89, 1899~1993!.

12H. S. P. Muller and M. C. L. Gerry, J. Chem. Phys.103, 577 ~1995!.13Y. Xu, W. Jager, and M. C. L. Gerry, J. Mol. Spectrosc.151, 206~1992!.14I. Merke and H. Dreizler, Z. Naturforsch.47a, 1141~1992!.15J. Haekel and H. Ma¨der, Z. Naturforsch.43a, 203 ~1988!.16I. Merke and H. Dreizler, Z. Naturforsch.43a, 196 ~1988!.17H. M. Pickett, J. Mol. Spectrosc.148, 371 ~1991!.18D. Christen, J. Mol. Struct.48, 101 ~1978!.19I. Mills, T. Cvitas, K. Homann, N. Kallay, and K. Kuchitsu,Quantities,Units and Symbols in Physical Chemistry, 2nd ed.~IUPAC, Blackwell,1993!.

20C. C. Costain, J. Chem. Phys.29, 864 ~1958!.21H. D. Rudolph, inAdvances in Molecular Structure Research, edited by I.Hargittai and M. Hargittai~JAI, Greenwich, CT!, Vol. 1.

22H. D. Rudolph, J. Mol. Spectrosc.89, 430 ~1981!.23K. J. Epple and H. D. Rudolph, J. Mol. Spectrosc.152, 355 ~1992!.24C. C. Costain, Trans. Am. Crystallogr. Assoc.2, 157 ~1966!.25H. D. Rudolph, J. Mol. Spectrosc.89, 460 ~1981!.26V. Typke, J. Mol. Spectrosc.72, 293 ~1978!.27K. Kuchitsu, J. Chem. Phys.49, 4456~1968!.28K. Kuchitsu and Y. Morino, Bull. Chem. Soc. Jpn.38, 805 ~1965!.29E. Tiemann, H. Kanamori, and E. Hirota, J. Mol. Spectrosc.137, 278

~1989!.30Y. Endo, K. Nagai, C. Yamada, and E. Hirota, J. Mol. Spectrosc.97, 213

~1983!.31H. S. P. Muller and M. C. L. Gerry, J. Chem. Soc. Faraday Trans.90,2601 ~1994!.

32M. Hargittai and I. Hargittai, J. Mol. Struct.73, 253 ~1981!.33W. D. Gwinn, J. Chem. Phys.55, 477 ~1971!.34F. J. Lovas and E. Tiemann, J. Phys. Chem. Ref. Data3, 609 ~1974!.35M. Fujitake and E. Hirota, J. Chem. Phys.91, 3426~1989!.36V. Jaccarino and J. G. King, Phys. Rev.83, 471 ~1951!.37C. D. Cornwell, J. Chem. Phys.44, 874 ~1966!.38R. E. Davis and J. S. Muenter, J. Chem. Phys.57, 2836~1972!.39B. Fabricant and S. Muenter, J. Chem. Phys.66, 5274~1977!.40W. H. Flygare, J. Chem. Phys.41, 793 ~1964!.41T. D. Gierke and W. H. Flygare, J. Am. Chem. Soc.94, 7277~1972!.42G. Malli and S. Fraga, Theor. Chim. Acta~Berl.! 5, 275 ~1966!.43R. J. Glinski, C. D. Taylor, and F. W. Kutzler, J. Phys. Chem.94, 6196

~1990!.44R. J. Colton and J. W. Rabelais, J. Electron Spectrosc. Relat. Phenom.3,345 ~1974!.

45A. Haas and H. Willner, Spectrochim. Acta34A, 541 ~1978!.46D. Bielefeldt and H. Willner, Spectrochim. Acta36A, 989 ~1980!.

10047J. Preusser and M. C. L. Gerry: FT microwave spectrum of ClSF

J. Chem. Phys., Vol. 106, No. 24, 22 June 1997 This article is copyrighted as indicated in the article. Reuse of AIP content is subject to the terms at: http://scitation.aip.org/termsconditions. Downloaded to IP:

155.247.166.234 On: Sat, 22 Nov 2014 10:03:48