Photodissociating trimethylamine at 193 nm to probe dynamics at a conical intersection and to calibrate detection efficiency of radical products

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Abstract

This paper reports crossed laser-molecular beam scattering experiments measuring the photofragment velocities and product branching in the photodissociation of trimethylamine (N(CH3)3) at 193 nm. We have observed two primary N–CH3 bond fission channels that ultimately produce different nitrogen-containing species, CH3+N(CH3)2 (X̃ 2B1); CH3+N(CH3)2*→CH3+CH2NCH3+H. The data also indicate that a third minor channel may contribute to the dissociation dynamics, CH3+N(CH3)2†→CH3+NC2H4+H2. The experiments show that ground state N(CH3)2 radicals are formed in the photodissociation, in sharp contrast to the exclusive production of NH2 (Ã 2A1) in a similar molecule, methylamine. We discuss how this results from the differing dynamics through the S1–S0 conical intersection in the exit channel in these two dissociating amines. We also use the photodissociation results to calibrate the mass spectrometric sensitivity at the m/e=15 daughter ion for methyl radicals vs N(CH3)2 and CH2NCH3 products. This provides the only necessary calibration to determine an absolute branching ratio in any system producing a methyl radical in one reaction channel and N(CH3)2 (X̃ 2B1) or CH2NCH3 in other reaction channels.

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