title: Synchrotron photoionization mass spectrometry measurements of kinetics and product formation in the allyl radical (H2CCHCH2) self-reaction.
abstract: Product channels for the self-reaction of the resonance-stabilized allyl radical, C3H5 + C3H5, have been studied with isomeric specificity at temperatures from 300-600 K and pressures from 1-6 Torr using time-resolved multiplexed photoionization mass spectrometry. Under these conditions 1,5-hexadiene was the only C6H10 product isomer detected. The lack of isomerization of the C6H10 product is in marked contrast to the C6H6 product in the related C3H3 + C3H3 reaction, and is due to the more saturated electronic structure of the C6H10 system. The disproportionation product channel, yielding allene + propene, was also detected, with an upper limit on the branching fraction relative to recombination of 0.03. Analysis of the allyl radical decay at 298 K yielded a total rate coefficient of (2.7 +/- 0.8) x 10(-11) cm(3) molecule(-1) s(-1), in good agreement with previous experimental measurements using ultraviolet kinetic absorption spectroscopy and a recent theoretical determination using variable reaction coordinate transition state theory. This result provides independent indirect support for the literature value of the allyl radical ultraviolet absorption cross-section near 223 nm.
authors.affiliation: Sandia National Laboratories, Combustion Research Facility, MS 9055, Livermore, California 94551-0969, USA.
authors.forename: Talitha M
authors.initials: TM
authors.lastname: Selby
authors.forename: Giovanni
authors.initials: G
authors.lastname: Meloni
authors.forename: Fabien
authors.initials: F
authors.lastname: Goulay
authors.forename: Stephen R
authors.initials: SR
authors.lastname: Leone
authors.forename: Askar
authors.initials: A
authors.lastname: Fahr
authors.forename: Craig A
authors.initials: CA
authors.lastname: Taatjes
authors.forename: David L
authors.initials: DL
authors.lastname: Osborn