Coherent vibrational dynamics of intermolecular hydrogen bonds in acetic aciddimers studied by ultrafast mid-infrared spectroscopy

Abstract

Ultrafast vibrational motions and the underlying microscopic couplings inhydrogen-bonded cyclic dimers of acetic acid are studied by pump–probe andphoton echo experiments in the mid-infrared. Upon femtosecond excitationof the O–H stretching mode, we demonstrate coherent nuclear motionsalong the in-plane dimer stretching mode which persist for picoseconds.The anharmonic coupling of the O–H stretching and the low-frequencymode is isolated in the nonlinear vibrational response, whereas othercouplings are suppressed. Three-pulse photon echo experiments demonstrate adephasing of O–H stretching excitations on a femtosecond timescale andquantum beats due to the anharmonically coupled dimer stretching mode.