Vibrational dynamics of benzoic acid in nonpolar solvents studied by subpicosecond infrared pump–probe spectroscopy

The vibrational dynamics of the OH stretching mode of the benzoic acid dimer in nonpolar solvents have been studied by subpicosecond, frequency-resolved infrared pump–probe spectroscopy. The signal consists of biexponential decay and a quantum beat, which is due to the intermolecular mode of the hydrogen bond coupled to the OH stretching mode. The subpicosecond component is suggested to be due to the vibrational relaxation of the low-frequency modes of the dimer, whereas the picosecond component is assigned to vibrational cooling. The frequency of the Fourier spectra of a quantum beat correlates with that of the OH stretching mode. The physical origin of the correlation is discussed.