Comment on: Structure of H2S–SO2Stephen G. Kukolich and Deanne J. Pauley Citation: The Journal of Chemical Physics 93, 871 (1990); doi: 10.1063/1.459464 View online: http://dx.doi.org/10.1063/1.459464 View Table of Contents: http://scitation.aip.org/content/aip/journal/jcp/93/1?ver=pdfcov Published by the AIP Publishing Articles you may be interested in Comment on: Resonance structure in the energy dependence of statetostate differential scattering crosssections for the D+H2(v,j)→HD(v’,j’)+H reaction J. Chem. Phys. 93, 5356 (1990); 10.1063/1.459658 The microwave spectrum and structure of the H2O–SO2 complex J. Chem. Phys. 91, 5887 (1989); 10.1063/1.457457 Microwave spectra and structure for SO2H2S, SO2HDS, and SO2D2S complexes J. Chem. Phys. 87, 3749 (1987); 10.1063/1.452929 Comment on: ‘‘Nickel–sulphate contacts and SO= 4–H2O interactions in aqueous solutions’’ J. Chem. Phys. 85, 3135 (1986); 10.1063/1.450979 Comments on ``On the Structure of the Isomers of N2F2'' J. Chem. Phys. 34, 2188 (1961); 10.1063/1.1731849

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Letters to the Editor

2p. Guyot-Sionnest, W. Chen, and Y. R. Shen, Phys. Rev. B 33, 8254 (1986).

3H. W. K. Tom, T. F. Heinz, and Y. R. Shen, Phys. Rev. Leu. 51, 1983 (1983); H. W. K. Tom and G. D. Aumiller, Phys. Rev. B33, 8818 (1986).

4R. K. Chang, J. Duccing, and N. Bloembergen, Phys. Rev. Leu. 6, 15 (1965); K. Kemnitz, K. Bhattacharyya, J. M. Hicks, G. R. Pinto, K. B. Eisenthal, and T. F. Heinz, Chern. Phys. Leu. 131, 285 (1986).

50. A. Koos and G. L. Richmond (unpublished). "E. D. Palik, Handbook of Optical Constants of Solids (Academic, New York, 1985), p. 294.

7Unfortunately the phase between X~~~ and {; is undetermined. However,

COMMENTS

Comment on: Structure of H2S-S02

Stephen G. Kukolich and Deanne J. Pauley

some insight as to the nature of the response may be gained by varying the nature of the adsorbate. The presence of an oxide layer at the surface is expected to decrease the dipolar SH surface response, X~~~ (Ref. 9). Ano­dic oxide formation on the Au ( 111) surface results in a 40% decrease in Ix~~ - a{; I (Ref. 5) and leads to the conclusion that Ix~~~ I> la{; I·

"D. A. Koos, V. L. Shannon, and G. L. Richmond, J. Phys. Chern. 94, 2091 (1990).

'P. Guyot-Sionnest and A. Tadjeddine, J. Chern. Phys. 92, 734 (1990). lOR. Georgiadis, G. A. Neff, and G. L. Richmond, J. Chern. Phys. 92, 4623

(1990).

Department o/Chemistry, University 0/ Arizona, Tucson, Arizona 85721

(Received 8 March 1990; accepted 23 March 1990

The structure of the H 2S-S02 complex was reported previously' based on pulsed-beam Fourier transform mea­surements of microwave rotational transitions. In a recent paper on H 20-S02, Matsumura, Lovas, and Suenram2 rean­alyzed data on H2S-S02. They obtained the same basic "stacked" structure with a plane of symmetry, but different values for the angles 0 (between the plane of S02 and the S-S line) and tP (between the H 2S plane and the S-S line). We reanalyzed the rotational constant data with a new fit program, and found a local minimum in the standard devi­ation with (Rss ,0,tP) = (3.67 A, 66°, 76°) which are close to our original values and yield a standard deviation for the fit of 4.4 MHz. Then, starting with different initial conditions, we obtained a fit with a lower standard deviation of 2. 7 MHz and parameters Rss = 3.45(1), 0 = 103(1)", and tP = 71(3)". These values are in better agreement with the values (3.534 A, 99°,57°) obtained by Matsumura et al. 2 We scanned through a wide range of initial conditions without finding other local minima with smaller or comparable stan­dard deviations. The modified "best fit" structure is shown in Fig. 1. This new structure is in better agreement with the Kraitchman analysis coordinates given earlier. '

I , I

O-'-S '/ o

An important point here is that there can be multiple minima in least squares fits to obtain structures with limited FIG. 1. Structure of the H 2S-S02 complex.

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Letters to the Editor

TABLE I. Measured and calculated "best fit" values in MHz, for rotational constants A, B, and C obtained in a least squares fit to measured values. The standard deviation for the fit was 2.7 MHz.

Rotational constant S02-H 2S S02-HDS S02-D2S

A (measured) 8447.3 8229.7 8017.6 A (calculated) 8446.5 8228.7 8019.4 B (measured) 1762.0 1738.0 1715.2 B (calculated) 1765.9 1739.0 1713.5 C (measured) 1538.5 1519.7 1501.2 C (calculated) 1539.8 1518.0 1497.2

isotopic data. Using a Kraitchman analysis in combination with the least squares fits can be a useful guide as indicated in Ref. 2. The fit results are shown in Tables I and II.

TABLE II. Structure parameters (see Ref. 1) for the H 2S-S02 complex, obtained by a least squares fit to the combinations of rotational constants shown in Table I. Listed, estimated error limits· are 2u, but uncertainties due to model errors and correlation effects could be as large as ± 6° for the angles 0 and t/J.

Structure parameter

R"

Present results·

71(3)" 103 ( I)"

3.45(1) A

Ref. 2

56.8°( II) 99.0"( 13)

3.534(3) A

'R. E. Bumgarner, D. J. Pauley, and S. O. Kukolich, J. Chern. Phys. 87, 3749 (1987).

2K. Matsumura, F. J. Lovas, and R. D. Suenram, J. Chern. Phys. 91, 5887 ( 1987).

Comment on: Observation of an excimer band of the ArOD van der Waals molecule

J. L. Lemaire, W.-U L. Tchang-Brillet, and F. Rostas DAMAp et URA 812 du CNRS, Observatoire de Paris-Meudon, 92195 Meudon Cedex, France

J. Rostas and N. Shafizadeh Laboratoire de Photo physique Moleculaire du CNRS, Batiment 213, Universite de Paris-Sud, 914050rsay, France

Michael C. Heavena)

Department oj Chemistry, Emory University, Atlanta, Georgia 30322

(Received 2 February 1990; accepted 9 March 1990)

In a recent paper l a spectrum attributed to bound-free excimer emission of the (ArOO)* van der Waals complex was reported. The spectrum consisted of three intense fea­tures, observed at 313.9,315.1, and 316 nm on the red side of the 00 (A-X, 0-0) transition. In these experiments· 00* (A) was formed by photodissociating 0 20 with two 266 nm photons from a quadrupled Y AG laser. Features assigned to the complex were only seen when 0 201 Ar mix­tures were photolyzed. The optimum signal was obtained from a mixture of 0.3 Torr 0 20 with 10 Torr Ar.

Bound-bound spectra of the Ar-OO A-X system have been observed by laser induced fluorescence in supersonic expansions.2

-5 Analysis of these spectra on the basis .of an

Ar-(OH) stretch model had led to a set of potential energy curves for the ground and excited states. 3 The observed bound-free emission I was reproduced by a simple diatomic stretch model using the above excited state potential. How­ever, the experimental ground state curve had to be replaced by another one derived by analogy with the 2~ + ground state of the isoelectronic ArF molecule. This implied that the ob­served transition was occurring between the lower vibration-

allevels of the linear excited state and a repulsive region of the ground state potential in bent geometry. The qualitative features of the bent ground state potential were later con­firmed by ab initio calculations6 and the parametric analysis of the experimental data.7 Considering the expected overlap between the upper and lower state wave functions and the expected equilibrium population of the excited ArOO spe­cies, the intensity of the bands could be explained only if the transition moment could be assumed to increase very mar­kedly at short internuclear distances. This assumption was

. considered plausible in view of the charge exchange admix­ture expected in the excited valence state of ArOO correlat­ing with the 00 (A 2~ +) asymptote.

A new series of experiments have been undertaken in view of recent results which indicate that the lifetimes of the v' = 4-6 levels of ArOH(OO) are not markedly different from those of unperturbed OH (A 2~ + ).8 This would imply that the transition moment should increase sharply in the vicinity of the minimum of the excited state of ArOO in order to remain compatible with the proposed interpreta­tion. It was felt necessary to measure directly the lifetime

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