A Crossed Molecular Beam and Ab-Initio Investigation of the Reaction of Boron Monoxide (BO; X2危+) with Methylacetylene (CH3CCH; X1A1): Competing

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• 作者：Surajit Maity ; Dorian S. N. Parker ; Beni B. Dangi ; Ralf I. Kaiser ; Stefan Fau ; Ajith Perera ; Rodney J. Bartlett
• 刊名：Journal of Physical Chemistry A
• 出版年：2013
• 出版时间：November 21, 2013
• 年：2013
• 卷：117
• 期：46
• 页码：11794-11807
• 全文大小：694K
• 年卷期：v.117,no.46(November 21, 2013)
• ISSN：1520-5215

文摘

The gas-phase reaction of boron monoxide (¹¹BO; X²危⁺) with methylacetylene (CH₃CCH; X¹A₁) was investigated experimentally using crossed molecular beam technique at a collision energy of 22.7 kJ mol^鈥? and theoretically using state of the art electronic structure calculation, for the first time. The scattering dynamics were found to be indirect (complex forming reaction) and the reaction proceeded through the barrier-less formation of a van-der-Waals complex (¹¹BOC₃H₄) followed by isomerization via the addition of ¹¹BO(X²危⁺) to the C1 and/or C2 carbon atom of methylacetylene through submerged barriers. The resulting ¹¹BOC₃H₄ doublet radical intermediates underwent unimolecular decomposition involving three competing reaction mechanisms via two distinct atomic hydrogen losses and a methyl group elimination. Utilizing partially deuterated methylacetylene reactants (CD₃CCH; CH₃CCD), we revealed that the initial addition of ¹¹BO(X²危⁺) to the C1 carbon atom of methylacetylene was followed by hydrogen loss from the acetylenic carbon atom (C1) and from the methyl group (C3) leading to 1-propynyl boron monoxide (CH₃CC¹¹BO) and propadienyl boron monoxide (CH₂CCH¹¹BO), respectively. Addition of ¹¹BO(X²危⁺) to the C1 of methylacetylene followed by the migration of the boronyl group to the C2 carbon atom and/or an initial addition of ¹¹BO(X²危⁺) to the sterically less accessible C2 carbon atom of methylacetylene was followed by loss of a methyl group leading to the ethynyl boron monoxide product (HCC¹¹BO) in an overall exoergic reaction (78 卤 23 kJ mol^鈥?). The branching ratios of these channels forming CH₂CCH¹¹BO, CH₃CC¹¹BO, and HCC¹¹BO were derived to be 4 卤 3%, 40 卤 5%, and 56 卤 15%, respectively; these data are in excellent agreement with the calculated branching ratios using statistical RRKM theory yielding 1%, 38%, and 61%, respectively.