Fourier transform infrared spectroscopy and ab initio theory of acid–hydrogen sulfide clusters: H2S–HCl, D2S–DCl and H2S–(HCl)2

Abstract

The rotationally resolved Fourier transform infrared (FTIR) spectrum of the ν_s HCl and DCl stretching bands for the hydrogen bonded complex H₂S–HCl and its isotopomer D₂S–DCl have been observed in a supersonic jet at 0.02 cm⁻¹ resolution. In the same experimental conditions, two additional bands observed without rotational structure in the HCl range of the dimer have been assigned to the cyclic trimer H₂S–(HCl)₂. The multidimensional coupling picture involving the donor stretch mode ν_s and low frequency intermolecular modes already evidenced in several medium strength hydrogen bonded complexes is beautifully confirmed by the observation of completely separated hot band progressions in the 198 K cell spectrum of both dimers. Based on our anharmonic adiabatic approach for the treatment of the coupled vibrations, absolute vibrational frequencies, diagonal and off-diagonal anharmonicities as well as rovibrational coupling constants obtained from analyses of several 2-D subspaces at MP2 and CCSD(T) level are in excellent agreement with spectroscopic results. In the case of small light complexes, the combination of elevated rotational constants and a negligible contribution of intramolecular vibrational redistribution (IVR) improve the reliability of predissociation lifetime measurements, estimated to 180 ps for H₂S–HCl and above 200 ps for D₂S–DCl.