title: Spectroscopic identification of the resonance-stabilized cis- and trans-1-vinylpropargyl radicals.
abstract: The cis-1-vinylpropargyl (cis-1VPR, cis-pent-4-en-1-yn-3-yl) and trans-1-vinylpropargyl (trans-1VPR, trans-pent-4-en-1-yn-3-yl) radicals, produced in a supersonically cooled hydrocarbon discharge, have been identified by a synergy of 2-dimensional fluorescence and ionization spectroscopies, revealing their electronic origin transitions at 21,232 and 21,645 cm(-1) respectively. These assignments are supported by an excellent agreement between calculated ground state frequencies of cis-1VPR and trans-1VPR with those obtained by dispersed fluorescence spectroscopy. In addition, high-resolution rotational contours of the two bands are well simulated using calculated X- and A-state trans-1VPR and cis-1VPR rotational constants. Finally, computed origin transition energies of these two isomers are within several hundred wavenumbers of the observed band positions. With the 1-phenylpropargyl radical, the 1VPR isomers are the second 1-substituted propargyl species to have been observed abundantly from a hydrocarbon discharge, while no 3-substituted analogue has been positively identified. This is likely due to the greater resonance stabilization energy of the 1-substituted species, arising from concerted delocalization of the unpaired electron over the vinyl and propargyl moieties.
authors.affiliation: School of Chemistry, The University of Sydney, NSW 2006, Australia.
authors.forename: Neil J
authors.initials: NJ
authors.lastname: Reilly
authors.forename: Masakazu
authors.initials: M
authors.lastname: Nakajima
authors.forename: Tyler P
authors.initials: TP
authors.lastname: Troy
authors.forename: Nahid
authors.initials: N
authors.lastname: Chalyavi
authors.forename: Kieran A
authors.initials: KA
authors.lastname: Duncan
authors.forename: Klaas
authors.initials: K
authors.lastname: Nauta
authors.forename: Scott H
authors.initials: SH
authors.lastname: Kable
authors.forename: Timothy W
authors.initials: TW
authors.lastname: Schmidt