Ultrafast redistribution of vibrational excitation of CH-stretching modes probed via anti-Stokes Raman scattering

Resonant infrared femtosecond light pulses in the 3 mu m region are used to excite specific CH-stretching modes of liquid 1,1,1-trichloroethane, cyclo pentane, and cyclohexane. The ultrafast redistribution of vibrational excit ation between different CH-stretching modes and the vibrational relaxation of these modes are monitored by spontaneous anti-Stokes Raman scattering of properly delayed and spectrally shaped probe pulses. The results are treat ed with a rate-equation system, yielding energy-redistribution and energy-r elaxation times.