Article
Photodissociation of acetylene: Determination of D 0 0 (HCC–H) by photofragment imaging
Journal of Chemical Physics
(1990)
Abstract
Acetylene cooled in a He supersonic expansion is photodissociated by excitation in the 201-
216 nm region of the A IAu - X 11;g+ transition. Subsequent ionization ofthe H-atom
fragments by 2 + 1 (243 nm) REMPI, and mass-selected ion imaging allows analysis of the
velocity distribution of H-atoms from the HCCH :- C2H + H process. Measurement of the
maximum ve.!ocity fo~ H atoms from this channel producetl by photodissociation of acetylene
through theA IAu - X 11;g+ V~K~, n V~K~, 2~ VgK ~ and VgK ~ vibronic transitions gives a
value for Dg (HCC-H) of 131 ± 1 kcallmol. Other channels producing hydrogen atoms
(including HC2 :-C2 + Hand HCCH:-HCCH+ :-C2H+ + H) are detected at all photon
fluxes used. These multi photon channels produce hydrogen atoms with higher translational
energy and therefore obscure measurement of the maximum velocity of H atoms produced by
single-photon dissociation of acetylene. Reduction of photon flux by more than two orders of
magnitude to -5 X 106 J/cm2 gives a background, multiphoton, H-atom intensity of <..7% of
the peak primary dissociation intensity. Because this multiphoton background limits the
detectability of fast H atoms from single-photon dissociation of acetylene, the dissociation
energy reported here is an upper limit. Calculations of potential rovibronic excitation of the
C2H fragment are discussed.
Disciplines
Publication Date
November, 1990
DOI
10.1063/1.458973
Publisher Statement
Copyright 1990 American Institute of Physics. This article may be downloaded for personal use only. Any other use requires prior permission of the author and the American Institute of Physics.
Citation Information
David P. Baldwin, Mark A. Buntine and David W. Chandler. "Photodissociation of acetylene: Determination of D 0 0 (HCC–H) by photofragment imaging" Journal of Chemical Physics Vol. 93 Iss. 9 (1990) p. 6578 - 6584 Available at: http://works.bepress.com/david-baldwin/3/