Picosecond vibrational energy transfer observed in the CH and OH stretching region of stearic acid dimers in liquid solution

Picosecond infrared double resonance spectroscopy was performed on stearic acid dimers in liquid solution in CCl4. The results give evidence for a redistribution of the vibrational energy among all CH stretching modes with individual time constants of a few picoseconds. In particular a redistribution time of 4+/-2 ps is obtained for the equilibration between the antisymmetric and symmetric CH2 stretching modes, and an effective lifetime of 14+/-2 ps for the whole CH stretching ensemble is derived. Furthermore the data indicate that the energy is efficiently transferred along the hydrocarbon chain, and that the CH3 endgroup has a key role in the energy transfer to the solvent; even the vibrational (OH stretching) modes in the doubly hydrogen-bonded dimer ring seem to dissipate their energy by transferring it to the CHx chains rather than directly to the solvent.