Microwave spectra and structure for SO2H2S, SO2HDS, and SO2D2S complexesR. E. Bumgarner, D. J. Pauley, and S. G. Kukolich Citation: The Journal of Chemical Physics 87, 3749 (1987); doi: 10.1063/1.452929 View online: http://dx.doi.org/10.1063/1.452929 View Table of Contents: http://scitation.aip.org/content/aip/journal/jcp/87/7?ver=pdfcov Published by the AIP Publishing Articles you may be interested in The microwave spectrum and structure of the methanolSO2 complex J. Chem. Phys. 103, 6440 (1995); 10.1063/1.470730 The microwave spectrum and structure of the H2O–SO2 complex J. Chem. Phys. 91, 5887 (1989); 10.1063/1.457457 Formation of HS− and DS− by Dissociative Attachment in H2S, HDS, and D2S J. Chem. Phys. 56, 2540 (1972); 10.1063/1.1677577 Mass Spectra and Metastable Transitions of H2S, HDS, and D2S J. Chem. Phys. 39, 3106 (1963); 10.1063/1.1734150 The Infrared Absorption Spectra of H2S, HDS and D2S J. Chem. Phys. 4, 625 (1936); 10.1063/1.1749758

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Microwave spectra and structure for S02---H2S, S02---HOS, and S02---02S complexes

R. E. Bumgarner, D. J. Pauley, and S. G. Kukolich Department a/Chemistry, University 0/ Arizona, Tucson, Arizona 85721

(Received 13 April 1987; accepted 16 June 1987)

Microwave spectra for the S02' .. H2S, S02' .. HDS, and S02' .. D2S complexes were measured using a pulsed beam, Fourier transform microwave spectrometer. Both a-dipole and c-dipole transitions were obtained. A total of 24 transitions were obtained for SOz' .. H 2S, yielding A = 8447.3(2), B = 1762.004(7), C = 1538.483(7) MHz, t::.J = 5.04(2), t::.JK = 65.46(9), t::.K = - 323(240), 8J = 0.63(1) and 15K = 38(3) kHz. For S02'" HDS, nine transitions yielded A = 8229.7( 6), B = 1737.99(1), C = 1519.69(2) MHz, t::.J = 4.4( 4) and t::.JK = 60(2) kHz, and for S02" . D2S, 11 transitions yielded A = 8017.6( 6), B = 1715.24(2), C = 1501.24(2) MHz, and t::.J = 3.8( 4), t::.JK = 51 (2) kHz. For the H2S data only, there are four possible structures for the complex which fit the data. When the deuterium isotope data are included, only two possible structures fit the data. There is only one structure which allows two O· .. H hydrogen bonds, and this is the structure we favor. This analysis basically gives a "stacked" structure with two o· .. H hydrogen bonds and a near van der Waals radius contact between the two sulfur atoms.

I. INTRODUCTION

Complex formation is believed to play an important role in many cases of interest in atmospheric chemistry. Acid rain formation has been asociated with interactions of S02' H20, and various nitrogen oxides. It is very likely that com­plex formation between reactants will have a substantial ef­fect on reaction rates and preferred reaction pathways. As a model system, we have looked at the SOrH2S complex.

were used in the "search" mode of operation. For the S02' .. HDS and SOz' .. DzS spectra, the deuterated hydro­gen sulfide was made using deuterated 10% sulfuric acid on ferrous sulfide. The deuterated hydrogen sulfide was dried by vacuum distillation. All frequency measurements were relative to a 1 MHz quartz oscillator which was periodically calibrated to WWVH at 60 kHz. The reference frequency accuracy was 1 X 10-9 or better.

Preliminary results for this complex were published re­cently l,2 indicating a nonplanar cyclic complex incorporat­ing two O· .. H hydrogen bonds. The present data support this basic structure, but better fits to the new larger data set are obtained if the H2S is tilted out of the plane of the two 0·' . H hydrogen bonds. The present structure allows a dis­tance of 3.67 A between the two sulfur atoms, indicating a possible S'" S interaction. This results in an unusual "stacked" structure with the possibility of interaction between three pairs of atoms. Some lines previously thought to be associated with hindered rotation or inversion 1 are now assigned to c-dipole transitions.2

II. EXPERIMENTAL

Measurements of microwave rotational transition fre­quencies were made using a pulsed-beam, Fourier transform spectrometer recently constructed at the University of Ari­zona. The basic design is similar to the original Flygare­Balle machine,3 but incorporates a number of modifications to improve the reliability, frequency range, and sensitivity. This spectrometer system is described elsewhere.4

The searches for lines were carried out using a 5 MHz digitizing rate and 512 points to record the FlD's. For accu­rate frequency measurements, a 20 MHz digitzing rate with 4096 points was used. The complexes were produced by ex­panding a mixture of 1 % S02 and 1 % H2S in :::::; 1 atm of Ar through the solenoid-operated pulsed valve (General Valve Corp. 9-181-100) with a 1 mm orifice. Pulse rates up to 5 Hz

The measured transition frequencies are given in Tables I, II, and III. There were 24 rotational transitions assigned for S02-H2S, 9 transitions for S02-HDS, and 11 transitions

TABLE I. Measured and calculated transition frequencies of H2S-S02 •

Measured Calculated Meas. - Calc. Transition (MHz) (MHz) (kHz) Dipole

1 (1,1 )-2(1,2) 6377.201 6377.200 1 a 1(0,1)-2(0,2) 6595.316 6595.316 0 a 2( 1,2)-3( 1,3) 9562.159 9562.158 1 a 2(0,2)-3(0,3) 9878.956 9878.957 -1 a 2(2,1 )-3(2,2) 9899.342 9899.344 -2 a 0(0,0)-1 (1,0) 10 209.380 10209.380 0 c 2(1,1 )-3(1,2) 10 232.047 10 232.046 1 a 3(1,3)-4( 1,4) 12742.863 12742.862 1 a 3(0,3 )-4(0,4) 13 145.913 13 145.915 -2 a 3(2,2)-4(2,3) 13 194.334 13 194.336 -2 a 3(3,1 )-4(3,2) 13 206.634 13 206.635 -1 a 3(3,0)-4(3,1) 13207.143 13 207.140 3 a 3(2,1 )-4(2,2) 13 249.078 13 249.076 2 a 6(1,5)-7(0,7) 13 366.447 13 366.448 -1 c 3( 1,2)-4( 1,3) 13 635.512 13 635.512 0 a 1 (0,1)-2(1,1) 13732.809 13732.813 -4 c 4(1,4 )-5 (1,5) 15918.093 15918.091 2 a 4(0,4)-5(0,5) 16391.050 16391.046 4 a 4(2,3)-5(2,4) 16485.229 16485.229 0 a 4(3,2)-5(3,3) 16512.041 16512.041 0 a 4(3,1 )-5 (3,2) 16513.807 16513.807 0 a 4(2,2)-5(2,3) 16594.083 16594.087 -4 a 4(1,3)-5(1,4) 17032.540 17032.540 0 a 2(0,2)-3( 1,2) 17369.548 17 369.543 5 c

J. Chem. Phys. 87 (7), 1 October 1987 0021-9606/87/193749-04$02.10 © 1987 American Institute of Physics 3749

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3750 Bumgarner, Pauley, and Kukolich: S02···H2S complexes

TABLE II. Measured and calculated transition frequencies ofHDS-S02.

Measured Calculated Meas. - Calc. Transition (MHz) (MHz) (kHz) Dipole

1(0,1)-2(0,2) 6509.811 6509.803 8 a 4(1,3)-5(0,5) 8421.260 8421.258 2 c 2(1,2)-3(1,3) 9441.409 9441.414 -5 a 2(0,2)-3(0,3) 9750.920 9750.924 -4 a 0(0,0)-1 (1,0) 9967.535 9967.532 3 c 2( 1,1 )-3( 1,2) 10 096.227 10 096.217 10 a 3(0,3)-4(0,4) 12975.624 12975.635 -11 a 3(2,2)-4(2,3) 13 023.494 13 023.459 35 a 3(2,1)-4(2,2) 13 077.368 13 077.402 - 34 a

for SOrDzS. Although precautions were taken to minimize the amount of exchangeable hydrogen in the preparatory apparatus and gas-handling system, SOz-HDS was always observable in the deuterated samples. The signal-to-noise ra­tio of the observed transitions was a factor of 20-50 less than typical Ar-HCI transitions, indicating either a low complex dipole or, more likely, a low concentration of complexes in the beam. This, combined with isotopic dilution and deuter­ium quadrupole broadening, makes observation of transi­tions for the deuterated species quite difficult. Standard de­viations for the measured transition frequencies were typically 5 kHz.

III. RESULTS AND DATA ANALYSIS

These complexes are near prolate asymmetric rotors and the spectra were fit to Watson's A-reduced Hamiltonian in the I r representation.5 For HzS-SOz' the rotational con­stantsA, B, and C and the five quartic distortion parameters, AJ , AJK , AK , bJ , bK , were fit simultaneously resulting in a standard deviation for the overall fit of 2.5 kHz. A and ilK

are highly correlated and the spectrum can be fit nearly as well (standard deviation 3 kHz) without the AK parameter. For HDS-SOz and DzS-SOz, the limited number of transi­tions precludes the inclusion of all five quartic distortion parameters and only A, B, C, AJ , and ilJK were fit for these species.

The rotational constants and distortion parameters are listed in Table IV. The reported uncertainties in the param­eters are two standard deviations of the fit except for the A

TABLE III. Measured and calculated transition frequencies of D 2S-S02.

Measured Calculated Meas. - Calc. Transition (MHz) (MHz) (kHz) Dipole

4(1,3)-5(0,5) 8430.091 8430.144 - 53 c 2( 1,2)-3( 1,3) 9324.423 9324.414 9 a 2(0,2)-3(0,3) 9627.637 9627.613 24 a 2(2,1 )-3(2,2) 9647.830 9647.803 27 a 2(2,0)-3(2,1) 9669.219 9669.214 5 a 0(0,0)-1 (1,0) 9732.754 9732.768 -14 c 2(1,1)-3(1,2) 9966.349 9966.325 24 a 5(1,4)-6(0,6) 10 951.151 10 951.112 39 c 3(1,3)-4(1,4) 12426.064 12406.068 -4 a 3(0,3)-4(0,4) 12 811.520 12 811.557 - 37 a 3(2,2)-4(2,3) 12859.096 12859.146 - 50 a

TABLE IV. Rotational and distortion constants obtained by fitting fre-quencies listed in Tables I, II, and III. Listed errors are 20", * indicates pa-rameter held equal to zero during fit.

S02' "H2S S02"'HDS S02" 'D2S

A(MHz) 8447.3(2) 8229.7(6) 8017.6(6) B(MHz) 1762.004(7) 1737.99(1 ) 1715.24(2) C(MHz) 1538.483(7) 1519.69(2) 1501.24(2) 6.J (kHz) 5.04(2) 4.4(4) 3.8(4)

6.JK (kHz) 65.46(9) 60(2) 51 (2) 6.K (kHz) - 323(240) * * 8J (kHz) 0.63(1 ) * * OK (kHz) 38(3) •

O"FIT (kHz) 2.5 26 42

rotational constants of HDS-SOz and DzS-SOz. The stan­dard deviation of A from the fits when ilK is not included is 0.04 MHz. This is not a realistic estimate of the uncertainty in A due to the previously mentioned correlation. For this reason, we report the uncertainty in A for HDS-SOz and DzS-SOz as twice the magnitude of ilK from the HzS-SOz fit or 0.6 MHz.

IV. STRUCTURE OF THE COMPLEX

Two experimental results which must be accounted for when considering a fit of possible structures to the available data are:

( 1) No b-dipole transitions were observed. The spectral fits of the HzS-SOz data allow a very accurate prediction of b-dipole transition frequencies and none of these transitions were observed despite extensive signal averaging. If the HzS­SOz complex has any b dipole at all, we made the conserva­tive estimate that its value can be no larger than 11 10th of the value of the a dipole. This estimate is based on the following: The a-dipole 2 (0,2 )-3 (0,3) transition at 9879 is observed at 5/1 S/N in a single gas pulse. The b-dipole 0(0,0)-1(1,1) line predicted at 9986 is not seen with 3600 gas pulses. The relative intensities of these lines for equal a and b dipoles assuming similar populations is 3/1 (a/b). Rotational cool­ing was not taken into account, but would enhance the rela­tive intensity of the b transition, resulting in a lower estimate of the maximum b dipole.

(2) Only two sets of transitions for the deuterated spe­cies were observed, one assignable to DzS-SOz and one to HDS-SOz' If the hydrogens of HzS are not in equivalent positions in the complex, we would expect two sets of trans i­tions for HDS-SOz and one set for DzS-SOz'

In all structure fits, we make the usual assumption that the structures of the monomers remain unchanged upon complexation. The structures of the monomers used in the fits are given in Table V. The conversion factor between mo­ments of inertia and rotational constants used is 505379.06 MHzamuAz.

When fitting only the SOz' .. HzS data, there are four structures which give exactly the same calculated rotational constants A, B, and C. This result is due to the fact that inversion of either SOz or HzS through its center of mass will not change the moment of inertia of the complex. Two of these four structures for the complex can be eliminated using

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Bumgarner, Pauley, and Kukolich: S02· .. H2S complexes 3751

TABLE V. Structures of the monomers (Ref. 8). Values are Ro-type pa­rameters.

R (S-X) Angle (X-S-X)

1.434 A 119.4'

H 2S

1.344 A 92.2'

the S02-HDS and S02-D2S data. The relatively small changes in (B + C) on deuteration favor the structure shown in Fig. 1, with the H atoms close to the center of mass of the complex. Inverting H 2S through its center of mass puts the H atoms much further from the center of mass of the complex, and then the same structure would not fit data for all three isotopic species. The S02 molecule, however, can be inverted through its center of mass and the same rotational constants for all isotopic species measured would be ob­tained. This would greatly increase the O' .. H distances, ef­fectively eliminating the two o· .. H hydrogen bonds. We,

o I

5

\ o

5 \ o

b

c

H \

-5 /

H

a

a

FIG. I. Structure of the S02-H2S complex. Top view along the c axis (up­per figure) and view along the b axis (center). The measured angles are (J = 69' between the S02 plane and S· .. S line and rP = 67' between the H2S plane and S"'S line (bottom figure). The circles indicate van der Waals radii of 1.45 'for H [N. L. Allinger, et al., J. Am. Chern. Soc. 90, 1199 (1968)], 1.50 A. for 0 and 1.80 A for S [A. Bondi, J. Phys. Chern. 68, 441 ( 1964)). The distance between the sulfur atoms is R" = 3.67 A.

TABLE VI. Structure parameters R", (J, and rP obtained by fitting all mea­sured rotational constants, and calculated rotational constants in MHz. Listed errors are 217. Deviations from the equilibrium structure could be larger than this due to large amplitude vibrations of the subunits.

Structure parameter

R" (J

rP

Rotational constant

A (Measured) A (Calculated)

B + C (Measured) B + C (Calculated) B - C (Measured) B - C (Calculated)

Value

3.67(3) A 69(4 )' 67(9)'

S02' .. H 2S S02' .. HDS S02' .. D2S

8447.3 8229.7 8017.6 8435.3 8229.4 8030.6 3300.5 3257.7 3216.5 3298.0 3251.4 3206.8

223.5 218.3 214.0 224.6 220.2 216.2

therefore, favor the structure shown in Fig. 1, with the struc­tural parameters from the fits given in Table VI. The Kraitchman analysis (see below) also favors this structure.

In fitting structures to observed rotational constants, it was found that the value of Rss is determined primarily by B + C of the complex, (J is determined by B - C and ifJ is most sensitive toA. We fit the structure by two methods and obtained essentially the same results. In the first method, we carried out a direct, least-squares fit of R ss , (J, and ifJ to the rotational constants for all isotopic data. In the second meth­od, Kraitchman analysis was used to locate the hydrogen atoms, then Rss and (J were determined by fitting rotational constants modified to remove the effect of the hydrogen atoms. In Table VI we present the structure parameters R ss ,

(J, and ifJ obtained by using the first method to fit the three observed isotopic species of S02' .. H 2S. When the isotopic forms are fit independently, the sulfur-sulfur distance R ss '

and the angle (J between the S02 b axis and R ss , remain fairly constant for the three species. The angle ifJ between the H 2S b axis and Rss varies considerably with isotopic substitution when the different isotopes are fitted separately, indicating a large amplitude vibration.

The uncertainties in Rss and (J obtained from the least squares fitting procedure are larger than expected from sta­tistical uncertainties in the data. This results from a correla­tion between R" and (J in the calculation of rotational con­stants. The highest uncertainty is in ifJ since it is most sensitive to effects of large amplitude vibrations of the hy­drogen atoms. The large amplitude vibrations in ifJ, com­bined with an asymmetric potential, could cause deviations of 10° or greater between equilibrium angles and the vibra­tionally averaged structure we obtain.

We have data for isotopic substitution of the hydrogen atoms, so a Kraitchman-type analysis6 was carried out to locate the hydrogen atoms and to check our proposed struc­ture. The magnitudes of the hydrogen atom coordinates aH ,

b H' and CH are given in Table VII for three substitution pairs. The standard6 single-substitution equations were used for S02-H 2S --+ S02-HDS and SOz-HDS --+ S02-D 2S.

For a molecule which is symmetric with respect to re-

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3752 Bumgarner, Pauley, and Kukolich: S02· .. H2S complexes

TABLE VII. Results of Kraitchman analysis and structure fit for isotopi­cally substituted S02-H2' aH , bH , and CH are the magnitudes of coordinates of the hydrogen atoms in the center of mass system.

Hydrogen atom coordinates (A) aH bH CH

Single substitution H 2S vs HDS 1.79 0.93 0.86 Single substitution HDS vs D2S 1.78 0.96 0.85 Double substitution H2S vs D2S 1.79 0.94 0.87 Structure fit result 1.97 0.97 0.77

flections in the a-c plane, it has been shown 7 that for a double substitution of an atom(j) not in the a-c plane:

I~a = Iaa + 2t::.mb I + J..l2CI,

Itb = Ibb + J..l2(aI + cI),

I~c = Icc + J..l2aI + 2t::.mb I,

I~c = J..l2aj Cj ,

where I ~x are the moments of inertia of the substituted mol­ecule in the principal axis frame of the parent molecule, t::.m = mD - mH and J..l2 = (2t::.mMp )j(2t::.m + M p ), where M p is the mass of the parent molecule. The results in Table VII are remarkably consistent, considering that the Kraitchman analysis depends on the structure being invar­iant to isotopic substitution.

The second method of obtaining the structure consists of using the above equations for a double substitution to remove the effects of the hydrogen atoms on the rotational constants for S02-H2S, In order to do this, we consider the S02-S skeleton as the "parent" molecule and S02-H2S as the "substituted" form. This results in effective rotational constants for the skeleton (S02-S) of A * = 8955.37, B* = 1811.03, and C* = 1577.04 MHz. These were fit to obtain the structure parameters R:; = 3.68(3)A and (}*=68(5)".

These are in good agreement with the results of method 1, indicating that the basic structure and orientation of the

H2S subunit is correct. As a further check, we can compute the H-S bond length in H2S from these fit results to be 1.41 A. This is longer than the experimental value ( 1.344 A) and indicates that we cannot locate the hydrogen atom to an accuracy better than about 0.1 A, in spite of the high degree of consistency of the Kraitchman analysis. We attribute this to vibrational effects, not a change in structure of H2S on complexation.

The stacked structure is consistent with a dipole-dipole interaction between S02 and H 2S contributing significantly to the binding. This effect probably gives a larger fractional contribution to the binding in this case since sulfuydral (S-H) hydrogen bonds are known to be much weaker than O-H hydrogen bonds. The observed hydrogen bond length of 3.1 (2) A is much longer than a typical hydrogen bond.

ACKNOWLEDGMENTS

This work was supported by the National Science Foun­dation. Acknowledgment is made to the donors of the Petro­leum Research Fund, administered by the American Chemi­cal Society, for partial support of this research. We thank Professor R. L. Kuczkowski for many helpful comments on this manuscript.

'D. J. Pauley, R. E. Bumgarner, and S. G. Kukolich, Chern. Phys. Lett. 132, 67 (1986).

2D. J. Pauley, R. E. Bumgarner, and S. G. Kukolich, Chern. Phys. Lett. 135, 486 (1987).

3T. J. Balle and W. H. Flygare, Rev. Sci. Instrum. 52, 33 (1981). 4R. E. Bumgarner and S. G. Kukolich, J. Chern. Phys. 86,1083 (1987). 5James K. G. Watson, 1. Chern. Phys. 48, 4517 (1968); James K. G. Wat­son, Vibrational Spectra and Structure, edited by James R. Durig (Else­vier, New York, 1977), Vol. 6, pp. 1-89.

6W. Gordy and R. L. Cook, Microwave Molecular Spectra, Vol. IX in Tech­nique of Organic Chemistry, edited by A. Weissberger (Interscience, New York, 1970), Chap. 3; J. Kraitchman, Am. J. Phys. 21,17 (1953).

7A. Chutjian, J. Mol. Spectrosc. 14, 361 (1964). 8M. D. Harmony, V. W. Laurie, R. L. Kuczkowski, R. H. Schwendeman, D. A. Ramsay, F. J. Lovas, W. 1. Lafferty, and A. G. Maki, J. Phys. Chern. Ref. Data 8,619 (1979).

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