Librational substructure of the OH-stretching band of an H-bonded dimer observed by time-resolved spectroscopy

The stretching mode of OH-groups with a proton donor function of an alcohol associating to open hydrogen-bonded dimers is investigated in the liquid p hase. Spectral holes with a frequency spacing of approximate to 35 cm(-1) i n the fundamental OH-transition and of approximate to 45 cm(-1) in the exci ted state-absorption are determined. This gives strong evidence for combina tion tones with the bending Vibration of the hydrogen bridge bond governing the dynamics and the shape of the proton donor OH-stretching band. The com bination modes display additional relaxation channels for the excited OH-st retching mode resulting in a lifetime shortening from 8 ps (monomer) down t o 3.6 ps (proton donor, 260 K). (C) 2000 Elsevier Science B.V. All rights r eserved.