title: Product branching fractions of the CH + propene reaction from synchrotron photoionization mass spectrometry.
abstract: The CH(X(2)Π) + propene reaction is studied in the gas phase at 298 K and 4 Torr (533.3 Pa) using VUV synchrotron photoionization mass spectrometry. The dominant product channel is the formation of C4H6 (m/z 54) + H. By fitting experimental photoionization spectra to measured spectra of known C4H6 isomers, the following relative branching fractions are obtained: 1,3-butadiene (0.63 ± 0.13), 1,2-butadiene (0.25 ± 0.05), and 1-butyne (0.12 ± 0.03) with no detectable contribution from 2-butyne. The CD + propene reaction is also studied and two product channels are observed that correspond to C4H6 (m/z 54) + D and C4H5D (m/z 55) + H, formed at a ratio of 0.4 (m/z 54) to 1.0 (m/z 55). The D elimination channel forms almost exclusively 1,2-butadiene (0.97 ± 0.20) whereas the H elimination channel leads to the formation of deuterated 1,3-butadiene (0.89 ± 0.18) and 1-butyne (0.11 ± 0.02); photoionization spectra of undeuterated species are used in the fitting of the measured m/z 55 (C4H5D) spectrum. The results are generally consistent with a CH cycloaddition mechanism to the C═C bond of propene, forming 1-methylallyl followed by elimination of a H atom via several competing processes. The direct detection of 1,3-butadiene as a reaction product is an important validation of molecular weight growth schemes implicating the CH + propene reaction, for example, those reported recently for the formation of benzene in the interstellar medium (Jones , B. M. Proc. Natl. Acad. Sci. U.S.A. 2011 , 108 , 452 - 457).
authors.affiliation: School of Chemistry, University of Wollongong, NSW 2522, Australia. adamt@uow.edu.au
authors.forename: Adam J
authors.initials: AJ
authors.lastname: Trevitt
authors.forename: Matthew B
authors.initials: MB
authors.lastname: Prendergast
authors.forename: Fabien
authors.initials: F
authors.lastname: Goulay
authors.forename: John D
authors.initials: JD
authors.lastname: Savee
authors.forename: David L
authors.initials: DL
authors.lastname: Osborn
authors.forename: Craig A
authors.initials: CA
authors.lastname: Taatjes
authors.forename: Stephen R
authors.initials: SR
authors.lastname: Leone