Time resolved incoherent anti-Stokes Raman spectroscopy of dichloromethane

Studies of vibrational relaxation processes of molecules in liquids require sophisticated experimental techniques. Using time resolved incoherent anti-Stokes Raman spectroscopy as detection process after a strong excitation of a well-defined vibrational state, detailed information about the relaxation pathways of vibrational energy is obtained. The experimental setup used for this study starts with a mode-locked Nd:YLF laser and uses a two-step parametric conversion stage to obtain the desired strong IR excitation pulses. The anti-Stokes scattering from the vibrationally excited molecules is detected with a CCD multichannel array behind a spectrometer, allowing the observation of the time evolution of complete Raman spectra. First results are presented for dichloromethane (CH2Cl2) showing that at least six of the nine fundamental vibrations are involved in the relaxation of the prepared CH2 stretching vibration. The observed time constants are compared with previous measurements.