title: Temperature-dependent kinetics of the vinyl radical (C2H3) self-reaction.
abstract: The rate coefficient for the self-reaction of vinyl radicals has been measured by two independent methods. The rate constant as a function of temperature at 20 Torr has been determined by a laser-photolysis/laser absorption technique. Vinyl iodide is photolyzed at 266 nm, and both the vinyl radical and the iodine atom photolysis products are monitored by laser absorption. The vinyl radical concentration is derived from the initial iodine atom concentration, which is determined by using the known absorption cross section of the iodine atomic transition to relate the observed absorption to concentration. The measured rate constant for the self-reaction at room temperature is approximately a factor of 2 lower than literature recommendations. The reaction displays a slightly negative temperature dependence, which can be represented by a negative activation energy, (E(a)/R) = -400 K. The laser absorption results are supported by independent experiments at 298 K and 4 Torr using time-resolved synchrotron-photoionization mass-spectrometric detection of the products of divinyl ketone and methyl vinyl ketone photolysis. The photoionization mass spectrometry experiments additionally show that methyl + propargyl are formed in the vinyl radical self-reaction, with an estimated branching fraction of 0.5 at 298 K and 4 Torr.
authors.affiliation: Department of Chemistry, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA.
authors.forename: Huzeifa
authors.initials: H
authors.lastname: Ismail
authors.forename: Paul R
authors.initials: PR
authors.lastname: Abel
authors.forename: William H
authors.initials: WH
authors.lastname: Green
authors.forename: Askar
authors.initials: A
authors.lastname: Fahr
authors.forename: Leonard E
authors.initials: LE
authors.lastname: Jusinski
authors.forename: Adam M
authors.initials: AM
authors.lastname: Knepp
authors.forename: Judit
authors.initials: J
authors.lastname: Zádor
authors.forename: Giovanni
authors.initials: G
authors.lastname: Meloni
authors.forename: Talitha M
authors.initials: TM
authors.lastname: Selby
authors.forename: David L
authors.initials: DL
authors.lastname: Osborn
authors.forename: Craig A
authors.initials: CA
authors.lastname: Taatjes