Infrared spectroscopic studies of hydrogen-bonded complexes in cryogenic sulutions

Abstract

We have measured the ν s(OH) band parameters of the IR absorption spectra for a wide variety of hydrogen-bonded (HB) complexes of CH 3OH(D), CF 3CH 2OH, and (CF 3) 3COH(D) with some simplest representatives of various classes of bases in Xe and Kr in the temperature range 120–270 K. The ν s(OH) absorption bands of the HB complexes in solution in atomic solvents have been demonstrated to be narrower by a factor of 2 to 4 than in molecular solvents at the same temperature. The fact that the ν s(OH) bandwidths in Xe and in the gas phase at similar temperatures are practically the same indicates that these bandwidths are in both cases governed mainly by the contribution of “hot transitions” from a sequence of excited levels of the ν β low-frequency bending mode of the hydrogen bond. The other characteristic features revealed for the complexes under study in liquid Xe and Kr at ν s(OH) frequency shifts up to 500 cm −1 include: (1) slight temperature dependence of the ν s(OH) bandwidth (0.1–0.3 cm −1/K), (2) almost “normal” isotope frequency ratio ν s(OH)/ν s(OD) (1.34–1.36) and (3) low ν s(OH) temperature shift values (0.1–0.4 cm −1/K).