High Power Picosecond Photolysis of Simple Organic Molecular Gases

Abstract

High-power picosecond UV pulses from a Nd:YAG modelocked laser were used to induce a visible emission from a variety of gaseous organic molecules.We report the observation of electronically excited C', CH, CN and H fragments. The spectral characteristics and :im development of the emitting species are highly dependent ( j uoon the structure of the parent molecules., cLaser Dhotolsis of simple molecules has contributed to a deeper understanding of dynamical processes in photodissociation. &N Our :oncern in the present work is with the decomoosition of sim-:ie compounds which afford generic models of processes important in explosives, fuels and other energetic materials.Multiphoton IR and JV laser dissociation (L-4) has previously been applied to study the primary decomposition processes of gas-phase hydrocarbons and subsequent reaction of fragments having significance in the kinetics or combustion. These experiments have been performed in the nanosecond time domain and at millitorr gas pressures in order to maintain a collision-free time regime during the duration of the exci:ation pulse.In our experiments the time resolution afforded by oicosecond pulse excitation enables such photoivsis even at atmospheric pressures, yielding high fragment concentrations. For the pressures and high flux densities employed in this work, multiohoton absorption processes can be accompanied by dielectric ireakdown (5).ndeed, since laser-induced breakdown is a nonresonant process, this very non-specificity facilitates the decomposition of a wide variety of materials.Here, we demonstrate the utility of the technique in generating :ragmencs w . se emission spectra reflect their orecursors.We .ave carried Out the pno:olvsis :f ketene, methane, carbon moncxioe L and ni-romechane at ressures in the range of 10-500 torr, and _s:ue'd the l'uminescence from 2, CH, CN and H fragments.