Vibrational dynamics of the hydrogen bond in H2S–HF: Fourier-transform-infrared spectra and ab initio theory

Abstract

The rotationally resolved infrared spectrum of the hydrogen bonded complex H₂S–HF and of its isotopomer D₂S–DF in the HF/DF stretching range have been observed in a supersonic jet Fourier-transform infrared (FTIR) experiment and indicate a predissociation lifetime of 130 ps for H₂S–HF. Complementary spectra taken at a temperature of 190 K in a cell without resolved rotational structure indicate the presence of strong anharmonic couplings between low frequency intermolecular modes and the HF donor stretch mode previously observed in other complexes with heavier acceptor molecules without rotational fine structure. The anharmonic analysis of the hot band progressions and of the rotational data confirm the coupling mechanism. The coupling constants and the absolute frequency of the hydrogen bonded stretch mode are in excellent agreement with theoretical predictions based on adiabatic variational calculations on potential surfaces computed at MP2 and CCSD(T) level. Complementary calculations with a perturbational approach further confirm the coupling model.