Ab initio rovibrational spectroscopy of hydrogen sulfide

Potential energy hypersurfaces (PES) have been constructed for the ground electronic state of ${\mathrm{H}}_{\mathrm{2}}\mathrm{S}$ utilizing results from state-of-the-art ab initio quantum chemical methods, most notably higher-order coupled cluster theory employing (core-polarized) correlation-consistent basis sets. Small corrections due to extrapolation to the complete basis set and full configuration interaction limits, core correlation, and relativistic corrections, as well as 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 different PESs. The final converged ab initio PES of this study reproduces the available vibrational band origins of ${\mathrm{H}}_{\mathrm{2}}{\mathrm{ }}^{\mathrm{32}}\mathrm{S},$ ${\mathrm{HD}}^{\mathrm{32}}\mathrm{S},$ ${\mathrm{D}}_{\mathrm{2}}{\mathrm{ }}^{\mathrm{32}}\mathrm{S},$ and ${\mathrm{H}}_{\mathrm{2}}{\mathrm{ }}^{\mathrm{34}}\mathrm{S}$ with maximum deviations, gradually increasing for increased vibrational excitation, of 29(14 300), 10(3800), 7(4600), and 12(6400) cm⁻¹, respectively, where the maximum energy above the zero-point energy is given in parentheses. The errors are considerably larger for the bending states than for the stretching states. Reproduction of rotational term values, given explicitly for $\text{J=17}$ of the vibrational ground state, shows remarkable agreement between experiment and the purely ab initio approach of this study.