RESONANT VIBRATIONAL DEPHASING INVESTIGATED BY HIGH-PRECISION FEMTOSECOND CARS

Using three-colour coherent anti-Stokes Raman scattering on the femtosecond time scale, the concentration dependence of the dephasing time T2 of the nu(2) mode of acetone is carefully studied at room temperature for isotopic dilution and the solvent CCl4. Theoretical arguments suggest that the measured isotopic dilution effect of 10.8 +/- 1% represents the contribution of resonant energy transfer via the repulsive part of the intermolecular potential to the total dephasing rate of the neat liquid. The steric factor S accounting for the smaller efficiency of non-collinear interactions as compared to head-on collisions is determined from the experimental data to be S = 0.12 +/- 0.01, in agreement with theoretical expectations.