Ab initio calculation of harmonic vibrational frequencies and intensities of molecules containing atoms of the third period of the periodic table. I. hydrogen sulfide and sulfur dioxide

Abstract

The effect of including polarization functions and electron correlation on ab initio calculations of the geometry, the harmonic vibration frequencies, and vibrational intensities is investigated for H2S and SO2 using GAUSSIAN 86. The starting basis sets were the standard 6–311Gxx and D95 bases. It is found that the first basis set gives good results at the MP2 level for the geometry and frequencies of hydrogen sulfide but is not adequate for the sulfur dioxide geometry. At the MP2 level there is a great improvement in quality of the results for H2S on adding multiple polarization functions to the D95 basis. None of the basis sets used gave good results for the vibrational intensities of H2S. In a preliminary investigation of the use of CI methods for predicting the geometry of SO2 it is found that the results of the CISD and CCD techniques are much better than those obtained by the MP2 procedure.