Dynamics in the Early Stages of Decomposition in Liquid Nitromethane and Nitromethane−Diethylamine Mixtures

Laser-initiated decomposition of single aerosol particles in the source region of a time-of-flight spectrometer, followed by vacuum ultraviolet laser ionization and mass analysis of the reaction products, reveals the identity of species formed in the early stages of condensed-phase decomposition in nitromethane and nitromethane−diethylamine mixtures. In pure nitromethane, the initial stages of decomposition are characterized by unimolecular processes. At near-threshold energies, the cleavage of the C−N bond to form CH 3 and NO 2 dominates the dynamics, and at higher energies we find evidence of rearrangement to methylnitrite, followed by the formation of CH 3 O and NO. In nitromethane seeded with 0.1% diethylamine, an additional channel is observed which produces ionic intermediates. Detection of protonated diethylamine and the nitromethane aci-anion confirm that an acid−base reaction is involved in this case. We also detect the radical anion, NO 2 -, whose production is correlated with an increase in methyl radical yield compared to the results for pure nitromethane. This correlation shows that NO 2 - is directly implicated in nitromethane decomposition. Furthermore, deuterium labeling studies indicate a hydrogen atom transfer reaction between the nitromethane aci-anion and neutral nitromethane that produces the weakly bound nitromethane anion, the precursor to CH 3 and NO 2 - . These data support and extend a sensitization mechanism proposed by Gruzdkov and Gupta [Gruzdkov, Y. A.; Gupta, Y. M. J. Phys. Chem. A 1998, 102, 2322] and discriminate against others.