Perturbation of the internal vibrations of (CH3)2S and (CH3)2Se in matrix-isolated complexes with H2O and HCl: Indirect evidence for the trans lone pair effect in (CH3)2X molecules

The formation of hydrogen-bonded complexes (CH₃)₂X ? HA is characterized by small frequency perturbations of the internal vibrations of the base molecules in a low-temperature matrix. Apart from the ν_CXC vibrations the largest shifts are measured in the ν_CH3 spectral region. The unexpected large blue shifts, Δν_CH, are interpreted as an indirect evidence for the existence of the trans lone pair effect in methyl chalcogenides. Additional support is obtained from a comparison between the complexes of HCl and H₂O with (CH₃)₂O, (CH₃)₂S, and CH₃OH.