Mode specific vibrational kinetics after intramolecular electron transfer studied by picosecond anti-Stokes Raman spectroscopy

Picosecond vibrational relaxation initiated by intramolecular electron back-transfer of Betaine 30 in propylene carbonate is studied by time-resolved anti-Stokes Raman scattering. We demonstrate for the first time distinct nonequilibrium populations of vibrational modes in the electronic ground state that persist up to 10 ps. The strongest Raman band at 1607 cm^-1 exhibits a rise time close to the electron transfer time of 1 ps, suggesting that this mode is involved in electron transfer. Vibrations between 400 and 1400 cm^-1 display slower rise times. Quasi-equilibrium populations of the Raman active modes are established after 10 ps.