Direct observation of the photodecomposition of liquid nitromethane under UV photolysis by sub-picosecond time-resolved CARS experiments

Abstract

Using a sub-picosecond CARS experiment we observed the direct photolysis of liquid nitromethane after pulse excitation at 299 nm. We measured the dynamical behaviour under excitation of three main ground-state Raman lines: the v(CN) mode at 917 cm −1, the v s (NO 2) and δ s (CH 3) modes near 1400 cm −1 and the V s(CH 3) 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 photolysis quantum yield at 299 nm of 24% ± 5%. A non-radiative de-excitation channel from the excited to the ground state has been observed and its possible role in the explosive process is discussed.