Ultrafast vibrational energy redistribution within C–H and O–H stretching modes of liquid methanol

An ultrafast IR–Raman technique is used to study fast redistribution of vibrational energy within CH and OH stretching vibrations of liquid methanol. The instantaneous population distribution throughout the entire CH and OH stretch region (2700–3700 cm−1) is probed simultaneously. The fast redistribution produces a nonthermal population distribution within CH and OH stretching excitations. The nonequilibrium CH stretch population occurs because different CH stretching modes have different lifetimes. The nonequilibrium OH stretch population occurs when OH stretching excitations that are pumped by the laser on the red edge of the band undergo spectral diffusion toward the band center.