Ab initio rovibrational spectroscopy of hydrogen sulfide

Potential energy hypersurfaces (PES) have been constructed for the ground e lectronic state of H2S utilizing results from state-of-the-art ab initio qu antum chemical methods, most notably higher-order coupled cluster theory em ploying (core-polarized) correlation-consistent basis sets. Small correctio ns due to extrapolation to the complete basis set and full configuration in teraction limits, core correlation, and relativistic corrections, as well a s effects beyond the Born-Oppenheimer approximation have been investigated and incorporated into the final PES. Using the exact rovibrational kinetic energy operator rovibrational energy levels have been computed with the dif ferent PESs. The final converged ab initio PES of this study reproduces the available vibrational band origins of H-2 S-32, (HDS)-S-32, D-2 S-32, and H-2 S-34 with maximum deviations, gradually increasing for increased vibrat ional excitation, of 29(14 300), 10(3800), 7(4600), and 12(6400) cm(-1), re spectively, where the maximum energy above the zero-point energy is given i n parentheses. The errors are considerably larger for the bending states th an for the stretching states. Reproduction of rotational term values, given explicitly for J=17 of the vibrational ground state, shows remarkable agre ement between experiment and the purely ab initio approach of this study. ( C) 2001 American Institute of Physics.