MILLIMETER-WAVE SPECTROSCOPY OF THE VINYL RADICAL GENERATED BY UV LASER PHOTOLYSIS IN A PULSED SUPERSONIC JET EXPANSION: DETERMINATION OF THE PROTON TUNNELING SPLITTING
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Date
2002
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Publisher
Ohio State University
Abstract
The rotational and proton tunneling spectra of the vinyl radical have been observed by millimeter-wave spectroscopy combined with a pulsed supersonic jet technique. The vinyl radical was generated by the 193 nm excimer laser photolysis of vinyl bromide. The pure rotational transitions, $N_{K_{a}K_{c}} = 1_{01} - 0_{00}, 2_{02} - 1_{01}, 3_{03} - 2_{02}$, and $4_{04} - 3_{03}$, observed in the frequency region of $60 - 250$ GHz, consisted of two components, $0^{+}$ and $0^{-}$, confirming the proton tunneling motion of the vinyl radical. The observed rotational lines were split into fine and hyperfine components due to the spin-rotation interaction and the spin-nuclear spin interaction of the acetylenic (CH) as well as methylenic $(CH_{2})$ protons. The pure rotational spectra for $K_{a} = 1$ were also observed both for the $0^{+}$ and $0^{-}$ components. The rotatinal constants, spin-rotation coupling constants, and hyperfine coupling constants for each tunneling components obtained were consistent with the results of the ESR spectroscopy in the Ar $matrix^{a}$ and the infrared diode laser $spectroscopy^{b}$. The b-typ Q-branch lines for the $0^{+} \leftarrow 0^{-}$ proton tunneling transition were observed around 200 GHz. The proton tunneling splitting was determined to be about $0.54 cm^{-1}$, and the barrier height of the double minimum potential to be about $1250 cm^{-1}$.
Description
$^{a}$P. H. Kasai, J. Am. Chem. Soc. 94, 5950 (1972) $^{b}$H. Kanamori, Y. Endo, and E. Hirota, J. Chem. Phys. 92, 197 (1990)
Author Institution: Department of Chemistry, Faculty of Science, Kyushu University 33
Author Institution: Department of Chemistry, Faculty of Science, Kyushu University 33