Photodissociating trimethylamine at 193 nm to probe dynamics at a conical intersection and to calibrate detection efficiency of radical products
- The James Franck Institute and Department of Chemistry, The University of Chicago, Chicago, Illinois 60637 (United States)
This paper reports crossed laser-molecular beam scattering experiments measuring the photofragment velocities and product branching in the photodissociation of trimethylamine (N(CH{sub 3}){sub 3}) at 193 nm. We have observed two primary N{endash}CH{sub 3} bond fission channels that ultimately produce different nitrogen-containing species, CH{sub 3}+N(CH{sub 3}){sub 2} ({tilde X} {sup 2}B{sub 1}); CH{sub 3}+N(CH{sub 3}){sub 2}{sup {asterisk}}{r_arrow}CH{sub 3}+CH{sub 2}NCH{sub 3}+H. The data also indicate that a third minor channel may contribute to the dissociation dynamics, CH{sub 3}+N(CH{sub 3}){sub 2}{sup {dagger}}{r_arrow}CH{sub 3}+NC{sub 2}H{sub 4}+H{sub 2}. The experiments show that ground state N(CH{sub 3}){sub 2} radicals are formed in the photodissociation, in sharp contrast to the exclusive production of NH{sub 2} ({tilde A} {sup 2}A{sub 1}) in a similar molecule, methylamine. We discuss how this results from the differing dynamics through the S{sub 1}{endash}S{sub 0} 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(CH{sub 3}){sub 2} and CH{sub 2}NCH{sub 3} 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(CH{sub 3}){sub 2} ({tilde X} {sup 2}B{sub 1}) or CH{sub 2}NCH{sub 3} in other reaction channels. {copyright} {ital 1999 American Institute of Physics.}
- OSTI ID:
- 365976
- Journal Information:
- Journal of Chemical Physics, Vol. 111, Issue 10; Other Information: PBD: Sep 1999
- Country of Publication:
- United States
- Language:
- English
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