2574
J. Phys. Chem. 1986, 90, 2574-2580 frequency for the similar mode. The difference is most likely due to the ring strain which one would expect to find in the 2pyrrolidinones. The normal-coordinate analyses thus demonstrate that the vibrations associated with the carbonyl groups for all of the molecules and with the amide groups of the 2-pyrrolidinones are dissimilar in comparison with many other amides.
N-methyl-2-pyrrolidinone.The force constants for the methylene and methyl groups are, with some slight differences, similar to those for n-paraffin~.'~Other force constants such as those for ring angle bends, torsions, and in-plane deformations are higher, reflecting the ring strain and the partial rigidity imposed upon the ring by the partial double bond character of the amide bond. The carbonyl in-plane and out-of-plane deformational modes were found to be at approximately 540 and 480 cm-', respectively, for all molecules examined in this work. The N-H in-plane deformation of 2-pyrrolidinone was found to be at 1370 an-'.For all of the 2-pyrrolidinones, the amide bond stretch was found to have a frequency a t or near 1500 cm-I, in contrast to simple, acyclic cis amides for which 1370 cm-' has been given as the
Acknowledgment. Considerable thanks are due to Professor H. L. Strauss of the Berkeley Chemistry Department and the National Science Foundation who provided the facilities and support for much of this work. I am also indebted to Jim Scherer of USDA, Albany, CA, who ran all of the Raman spectra reported in this paper.
Photoelectron Spectroscopy of SO2-, Sa-, and S20Mark R. Nimlos and G. Barney Ellison* Department of Chemistry and Biochemistry, University of Colorado, Boulder, Colorado 80309 (Received: October 9, 1985)
We have studied the photoelectron spectroscopy of SO2-, S;, and SzO-and found the following electron affinities: EA(SOZ) = 1.107 f 0.008 eV, EA&) = 2.093 f 0.025 eV, EA(S20) = 1.877 f 0.008 eV. The heats of formation of the negative ions were determined to be AHf0298(S0;) = -98.0 0.2 kcal/mol, AHf0298(s3-) = -18.0 0.6 kcal/mol, AHfo298(S20-) = -57.5 f 0.3kcal/mol. From a Franckcondon analysis of the photoelectron spectra, we obtained the following geometrical parameters: rs-&O;) = 1.523 0.020 A, aGs-&Oz-) = 115.6 f 2.0°, rs-s(S3) = 1.90 0.05 R, rs-s(SzO-)= 2.010 0.020 A.
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Introduction Sulfur oxides are thought to be important as possible intermediates in the oxidation of organosulfur compounds.' Their corresponding negative ions are crucial species in a number of solution and solid-phase systemd In this paper, photoelectron spectroscopy is used to probe SOz-, S3-,and S20- and their resulting neutral molecules. From the spectra, electron affinities (EA) of the neutral molecules and vibrational frequencies of the neutral molecules and negative ions can be obtained. We also report heats of formation of these ions. These ions and their corresponding neutral molecules provide an interesting comparison to O3and O
