PHOTODISSOCIATION DYNAMICS OF THE PHENYL RADICAL VIA PHOTOFRAGMENT TRANSLATIONAL SPECTROSCOPY
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Date
2010
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Publisher
Ohio State University
Abstract
Photofragment translational spectroscopy was used to study the photodissociation dynamics of the phenyl radical at 193 and 248 nm. Time of flight data collected for the C$_6$H$_4$, C$_4$H$_3$, and C$_2$H$_2$ photofragments show the presence of two decomposition channels. The only C$_6$H$_5$ decomposition channel observed at 248 nm corresponds to C ??H bond fission from the cyclic radical producing $ortho$-benzyne. The translational energy distribution peaks at 0 $kcal/mol$ and is consistent with no exit barrier for the H loss process. At 193 nm photodissociation, however, H loss was observed to be the minor channel, while the major decomposition pathway corresponds with decyclization of the C$_6$H$_5$ radical and subsequent fragmentation to $n$-C$_4$H$_3$ and C$_2$H$_2$. These two momentum matched photofragments have a translational energy distribution that peaks around 9 $kcal/mol$, indicative of a process that proceeds through a tighter transition state. Previous theoretical work on the unimolecular decomposition of the phenyl radical \textbf{1997}, 101, 6790.} predicts a second H loss process that occurs after C$_6$H$_5$ decyclization resulting in the linear C$_6$H$_4$ photofragment. This channel cannot be unambiguously discerned from the C$_6$H$_4$$^+$ time of flight data, but is believed to take place since decyclization is observed.
Description
Author Institution: College of Chemistry, University of California, Berkeley, California 94720, and Chemical Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA