Crossed beam reaction of cyano radicals with hydrocarbon molecules. II. Chemical dynamics of 1-cyano-1-methylallene (CNCH{sub 3}CCCH{sub 2}; Xthinsp{sup 1}A{sup {prime}}) formation from reaction of CN(Xthinsp{sup 2}{Sigma}{sup +}) with dimethylacetylene CH{sub 3}CCCH{sub 3}
- Institute of Atomic and Molecular Sciences, 1, Section 4, Roosevelt Road, 107 Taipei, Taiwan, Republic of (China)
- Center for Computational Quantum Chemistry, Athens, Georgia 30602 (United States)
The reaction dynamics to form the 1-cyano-1-methylallene isomer CNCH{sub 3}CCCH{sub 2} in its {sup 1}A{sup {prime}} ground state via the radical{endash}closed shell reaction of the cyano radical CN(X&hthinsp;{sup 2}{Sigma}{sup +}) with dimethylacetylene CH{sub 3}CCCH{sub 3}&hthinsp;(X&hthinsp;{sup 1}A{sub 1}{sup {prime}}) are unraveled in a crossed molecular beam experiment at a collision energy of 20.8 kJ&hthinsp;mol{sup {minus}1} together with state-of-the-art electronic structure and Rice{endash}Ramsperger{endash}Kassel{endash}Marcus (RRKM) calculations. Forward convolution fitting of the laboratory angular distribution together with the time-of-flight spectra verify that the reaction is indirect and proceeds by addition of the CN radical to the {pi} orbital to form a cis/trans CH{sub 3}CNC{double_bond}CCH{sub 3} radical intermediate. This decomposes via a rather lose exit transition state located only 6{endash}7 kJ&hthinsp;mol{sup {minus}1} above the products to CNCH{sub 3}CCCH{sub 2} and atomic hydrogen. The best fit of the center-of-mass angular distribution is forward{endash}backward symmetric and peaks at {pi}/2 documenting that the fragmenting intermediate holds a lifetime longer than its rotational period. Further, the hydrogen atom leaves almost perpendicular to the C{sub 5}H{sub 5}N plane resulting in sideways scattering. This finding, together with low frequency bending and wagging modes, strongly support our electronic structure calculations showing a H{endash}C{endash}C angle of about 106.5{degree} in the exit transition state. The experimentally determined reaction exothermicity of 90{plus_minus}20&hthinsp;kJ&hthinsp;mol{sup {minus}1} is consistent with the theoretical value, 80.4 kJ&hthinsp;mol{sup {minus}1}. Unfavorable kinematics prevent us from observing the CN versus CH{sub 3} exchange channel, even though our RRKM calculations suggest that this pathway is more important. Since the title reaction is barrierless and exothermic, and the exit transition state is well below the energy of the reactants, this process might be involved in the formation of unsaturated nitriles even in the coldest interstellar environments such as dark, molecular clouds and the saturnian satellite Titan. {copyright} {ital 1999 American Institute of Physics.}
- OSTI ID:
- 692526
- Journal Information:
- Journal of Chemical Physics, Vol. 111, Issue 16; Other Information: PBD: Oct 1999
- Country of Publication:
- United States
- Language:
- English
Similar Records
Crossed beam reaction of cyano radicals with hydrocarbon molecules. I. Chemical dynamics of cyanobenzene (C[sub 6]H[sub 5]CN; X[sup 1]A[sub 1]) and perdeutero cyanobenzene (C[sub 6]D[sub 5]CN; X[sup 1]A[sub 1]) formation from reaction of CN(X[sup 1])
Elucidating the Chemical Dynamics of the Elementary Reactions of the 1-Propynyl Radical (CH3CC; X2A1) with Methylacetylene (H3CCCH; X1A1) and Allene (H2CCCH2; X1A1)