IONIZATION-LOSS STIMULATED RAMAN-SPECTROSCOPY OF JET-COOLED HYDROGEN-BONDED COMPLEXES CONTAINING PHENOLS

Stimulated Raman spectra of a variety of hydrogen-bonded, one-to-one complexes of phenol and substituted phenols are presented and discussed. The Raman spectra were recorded with ionization-loss stimulated Raman spectroscopy on supersonic molecular beam samples. Complexation-induced vibrational frequency shifts and vibrational line widths are reported for both the proton-donating moieties (the phenols) and the proton-accepting moieties in the complexes. The vibrational frequency shifts are discussed in terms of the strength of the hydrogen bond and the usefulness of different vibrational modes as indicators of hydrogen bonding. Particular attention is paid to the phenolic CO and OH stretch fundamentals. The line-width measurements suggest that vibrational modes closely associated with the hydrogen bond (i.e., the phenolic CO and OH stretches) relax more efficiently than other modes in the complexes. Even so, the lifetimes of the excited OH stretches are at least a few picoseconds for several of the complexes. Evidence for mode selective dynamics in the OH stretch region of the substituted phenol-water complexes is also presented and discussed.