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Author Ahmed, M. ♦ Peterka, D. S. ♦ Suits, A. G.
Source United States Department of Energy Office of Scientific and Technical Information
Content type Text
Language English
Subject Keyword CHEMISTRY ♦ ORGANIC COMPOUNDS ♦ RADICALS ♦ EXCITED STATES ♦ PHOTOLYSIS ♦ VINYL RADICALS ♦ MOLECULAR BEAMS ♦ FORMATION HEAT ♦ REACTION INTERMEDIATES ♦ VINYLIDENE RADICALS ♦ ACETYLENE ♦ DISSOCIATION ♦ FAR ULTRAVIOLET RADIATION
Abstract The technique of velocity map imaging (VELMI) has been applied to study the photodissociation of the vinyl radical (C{sub 2}H{sub 3}) at 243.2 nm in a molecular beam. Using momentum conservation, we show that the primary product is singlet vinylidene [H{sub 2}CC({tilde X}{sup 2}A{sup {prime}})], or singlet acetylene at energies where interconversion between the H{sub 2}CC and HCCH geometries is facile. In addition, a minor contribution is seen which is assigned to triplet acetylene [C{sub 2}H{sub 2}({tilde a}{sup 3}B{sub 2})]. We argue that out-of-plane motion of the third H atom is necessary to bring the excited states, of A{sup {double_prime}} symmetry, to an A{sup {prime}} symmetry leading to products, and the observed tranlsational energy distribution may show evidence of the barrier to this process. The heat of formation of vinylidene is derived to be 100.3{plus_minus}4.0 kcal/mol, in agreement with literature values. From the translational energy release, we derive the T{sub 0} for triplet acetylene C{sub 2}H{sub 2}({tilde a}{sup 3}B{sub 2}) to be 28&hthinsp;900 cm{sup {minus}1}, which does not agree well with recent {ital ab initio} calculations. Possible reasons for the disagreement are discussed. {copyright} {ital 1999 American Institute of Physics.}
ISSN 00219606
Educational Use Research
Learning Resource Type Article
Publisher Date 1999-03-01
Publisher Place United States
Journal Journal of Chemical Physics
Volume Number 110
Issue Number 9


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