IR Spectra and dipole moment function of the H2S molecule in the gas and liquid phases

The IR spectra of H2S molecules in the gas and liquid phases and in solutions of liquefied noble gases are experimentally studied over a wide range of frequencies, including the regions of second- and third-order transitions. Based on experimental data on the parameters of the effective dipole moment, the first, second, and third derivatives of the dipole moment of the H2S molecule with respect to the normal coordinates are recovered. The values of the first derivatives with respect to the coordinates associated with the stretching vibration are abnormally small in comparison with the higher-order derivatives. The change in the dipole moment of the molecule H2S under the influence of the intermolecular forces on gas-liquid transition is examined. The observed anomalously large (more than 200-fold) increase in the absolute intensity of the fundamental stretching vibration band nu(str) cannot be accounted for by abnormally strong intermolecular interaction forces. The increase in the absolute intensity of the nu(str) band is associated with abnormally small first derivatives of the dipole moment of the gas-phase molecule. The effect of the intermolecular forces on the dipole moment is compared to that for the H2O molecule.