Ab initio dipole moment functions of H232S and intensity anomalies in rovibrational spectra

Intensities of fundamental and of two-quanta overtone and combination rovibrational bands of H2S have been evaluated from electric dipole moment functions calculated using ab initio coupled-clusters methods. Particular features and derivatives of the dipole moment are discussed in relation with observed intensity anomalies in infrared spectra of this molecule. Rovibrational energy levels and corresponding eigenfunctions have been obtained variationally using an empirical potential energy function. Calculated absolute line intensities are compared with available experimental data. The generated electric dipole moment functions have allowed to considerably improve upon previous ab initio intensity calculations for fundamental bands, and to describe for the first time major observed anomalies in intensity distributions of H2S rovibrational bands. Discrepancies between ab initio and empirical values of the integrated band intensities are 12%, 8%, and 10% for the first triad bands ν1, ν3, 2ν2 and 4% and 6% for the strongest bands ν2+ν3 and ν1+ν2.