The 213. 8-nm photochemistry of gaseous 1,3-butadiene and the structure of some C sub 3 H sub 3 radicals

Journal Article · Wed Jan 10 23:00:00 EST 1990 · Journal of Physical Chemistry; (USA)

DOI:https://doi.org/10.1021/j100364a020· OSTI ID:6946646

Collin, G J; Deslauriers, H ^[1]; De Mare, G R ^[2]; Poirier, R A ^[3]

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1. Universite du Quebec a Chicoutimi (Canada)
2. Universite Libre de Bruxelles (Belgium)
3. Memorial Univ. of Newfoundland, Saint-John's (Canada)

A systematic study of the 213.8-nm (zinc line) photochemistry of 1,3-butadiene has been made either in the absence or in the presence of various additives--such as radical scavengers (O{sub 2}, NO, DI) and collisional quenchers--in the gas phase (pressure between 1 and 500 Torr). The major fate of the photoexcited 1,3-butadiene molecule is isomerization to the 1,2-butadiene structure which may then decompose to methyl and C{sub 3}H{sub 3} radicals ({Phi} = 0.64 {plus minus} 0.04 at 1 Torr of 1,3-butadiene). Minor processes include decomposition to the acetylene + ethylene couple ({Phi} = 0.22 {plus minus} 0.02) or to vinylacetylene ({Phi} = 0.038 {plus minus} 0.003) and molecular hydrogen. These two minor processes occur from different excited states. Some 2-butyne ({Phi} < 0.015) is formed by a unimolecular isomerization process. The photolysis of 1,3-butadiene-1,1,4,4-d{sub 4} indicates that at least three different intermediates are involved in the formation of molecular ethylene and acetylene. The C{sub 3}H{sub 3} radicals are not easily intercepted by DI: k(C{sub 3}H{sub 3} + DI) = 0.09 {plus minus} 0.03. Also at 21{degree}C and for (DI)/(1,3-butadiene) = 10, the highest ratio used {Phi}(allene + propyne)/{Phi}(CH{sub 3}D) = 0.72 and a fraction of the C{sub 3}H{sub 3} radicals are still not accounted for (reaction with 1,3-butadiene and/or recombination ). The relative energies obtained by ab initio RHF-SCF geometry optimizations for the doublet electronic state of the C{sub 3}H{sub 3} radical structures are E(propargyl) < E(propyn-1-yl) < E(cyclopropen-1-yl) < E(allenyl). General valence bond geometry optimizations and a multiconfigurational self-consistent-field surface scan also show that the propargyl species ({sup 2}B{sub 1} state) is the lowest energy one. There are probably at least two distinct C{sub 3}H{sub 3} radical structures (different states) present in the far-UV photolysis of 1,3-butadiene.

• OSTI ID: 6946646
• Journal Information: Journal of Physical Chemistry; (USA), Journal Name: Journal of Physical Chemistry; (USA) Vol. 94:1; ISSN JPCHA; ISSN 0022-3654
• Country of Publication: United States
• Language: English

Related Subjects

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
400500* -- Photochemistry
ALKENES
ALKYL RADICALS
BUTADIENE
CALCULATION METHODS
CHEMISTRY
COMPUTER CODES
DATA
DATA ANALYSIS
DIENES
ETHYLENE
EXPERIMENTAL DATA
HYDROCARBONS
INFORMATION
MEASURING INSTRUMENTS
MEASURING METHODS
NUMERICAL DATA
ORGANIC COMPOUNDS
PHOTOCHEMISTRY
POLYENES
PROPYL RADICALS
RADICALS
STRUCTURAL CHEMICAL ANALYSIS
THEORETICAL DATA