DIRECT OBSERVATION OF THE PHOTODECOMPOSITION OF LIQUID NITROMETHANE UNDER UV PHOTOLYSIS BY SUBPICOSECOND TIME-RESOLVED CARS EXPERIMENTS

Using a sub-picosecond CARS experiment we observed the direct photolys is of liquid nitromethane after pulse excitation at 299 nm. We measure d the dynamical behaviour under excitation of three main ground-state Raman lines: the nu(CN) mode at 917 cm(-1), the nu(s) (NO2) and delta( s) (CH3) modes near 1400 cm(-1) and the nu(s)(CH3) mode at 2968 cm(-1) . From the evolution of these modes we deduced that the excited state disappears with a lifetime of 1.1+/-0.3 ps and we measured a photolysi s quantum yield at 299 nm of 24%+/-5%. A non-radiative de-excitation c hannel from the excited to the ground state has been observed and its possible role in the explosive process is discussed.