ACCURATE AB-INITIO QUARTIC FORCE-FIELDS FOR THE SULFUR-COMPOUNDS H2S, CS2, OCS, AND CS

The quartic force fields of the H2S, CS2, OCS, and CS molecules have been computed using the CCSD(T) augmented coupled cluster method and spdf and spdfg basis sets. Neglect of core correlation results in fairly noticeable error in computed geometries, but does not seem to affect other spectroscopic constants substantially. Computed results for H2S are in excellent agreement with experiment; of the available experimental force fields, our calculations favor the very recent one by Kozin and Jensen. Good agreement is also seen for CS2, except for the sigma(g) stretch. After correction for multiple Fermi resonances, excellent results are also obtained for OCS. Residual error in CS can be traced back almost entirely to overestimation of the bond distance. (C) 1995 Academic Press, Inc.