An ab initio study of the structure and torsional modes of the H2SO4 molecule

Abstract

Ab initio calculations at the STO--3G and 4--31G levels have been carried out for the H2SO4 molecule as a function of the pair of twist angles of the H---O bonds about the respective O---S bonds. Values for the remaining bond angles and lengths were taken from the recent microwave structural determination by Kuczkowski et al. The results indicate a minimum energy for a structure with a (sc, sc) conformation and C2 symmetry, where sc denotes synclinal, or gauche. This structure corresponds to that observed. At a higher energy of 11.5 kJ mol-1 (4--31G) there is a structure with a (+sc, -sc) conformation and Cs symmetry. The torsional modes corresponding to the a and b irreducible representations of the C2 point group are estimated to have frequencies of 280 and 265 cm-1, respectively.