Ultrafast vibrational dynamics and solvation complexes of methyl acetate in methanol studied by sub‐picosecond infrared spectroscopy

The vibrational dynamics of the CO stretching mode of methyl acetate (MA) in methanol was studied by time‐resolved infrared (IR) pump‐probe spectroscopy. The vibrational energy relaxation (VER) process includes two components with time constants of 1.3 ± 0.1 and 4.0 ± 0.2 ps. These components result from the vibrational excitations of the hydrogen‐bonding complex of MA with one methanol and the MA monomer, respectively. The difference in the VER time is explained by the increase of the vibrational density of states (VDOS) by the intermolecular hydrogen bond. The time constants and the decay‐associated spectra are almost identical between the CH3OH and the CH3OD solutions. The vibrational modes localized in the intramolecular OH/OD bond of the solvent methanol have little effect on the vibrational dynamics of MA.