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})

Journal Article · Fri Oct 01 00:00:00 EDT 1999 · Journal of Chemical Physics

DOI:https://doi.org/10.1063/1.480070· OSTI ID:698895

Balucani, N; Asvany, O; Chang, A H; Lin, S H; Lee, Y T; Kaiser, R I ^[1]; Bettinger, H F; Schleyer, P v; Schaefer, III, H F ^[2]

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1. Institute of Atomic and Molecular Sciences, 1, Section 4, Roosevelt Road, 107 Taipei, Taiwan, Republic of (China)
2. Center for Computational Quantum Chemistry, The University of Georgia, Athens, Georgia 30602 (United States)

The chemical reaction dynamics to form cyanobenzene C{sub 6}H{sub 5}CN(X&hthinsp;{sup 1}A{sub 1}), and perdeutero cyanobenzene C{sub 6}D{sub 5}CN(X&hthinsp;{sup 1}A{sub 1}) via the neutral{endash}neutral reaction of the cyano radical CN(X&hthinsp;{sup 2}{Sigma}{sup +}), with benzene C{sub 6}H{sub 6}(X&hthinsp;{sup 1}A{sub 1g}) and perdeutero benzene C{sub 6}D{sub 6}(X&hthinsp;{sup 1}A{sub 1g}), were investigated in crossed molecular beam experiments at collision energies between 19.5 and 34.4 kJ&hthinsp;mol{sup {minus}1}. The laboratory angular distributions and time-of-flight spectra of the products were recorded at mass to charge ratios m/e=103{endash}98 and 108{endash}98, respectively. Forward-convolution fitting of our experimental data together with electronic structure calculations (B3LYP/6{minus}311+G{sup {asterisk}{asterisk}}) indicate that the reaction is without entrance barrier and governed by an initial attack of the CN radical on the carbon side to the aromatic {pi} electron density of the benzene molecule to form a C{sub s} symmetric C{sub 6}H{sub 6}CN(C{sub 6}D{sub 6}CN) complex. At all collision energies, the center-of-mass angular distributions are forward{endash}backward symmetric and peak at {pi}/2. This shape documents that the decomposing intermediate has a lifetime longer than its rotational period. The H/D atom is emitted almost perpendicular to the C{sub 6}H{sub 5}CN plane, giving preferentially sideways scattering. This experimental finding can be rationalized in light of the electronic structure calculations depicting a H{endash}C{endash}C angle of 101.2{degree} in the exit transition state. The latter is found to be tight and located about 32.8 kJ&hthinsp;mol{sup {minus}1} above the products. Our experimentally determined reaction exothermicity of 80{endash}95 kJ&hthinsp;mol{sup {minus}1} is in good agreement with the theoretically calculated one of 94.6 kJ&hthinsp;mol{sup {minus}1}. Neither the C{sub 6}H{sub 6}CN adduct nor the stable iso cyanobenzene isomer C{sub 6}H{sub 5}NC were found to contribute to the scattering signal. The experimental identification of cyanobenzene gives a strong background for the title reaction to be included with more confidence in reaction networks modeling the chemistry in dark, molecular clouds, outflow of dying carbon stars, hot molecular cores, as well as the atmosphere of hydrocarbon rich planets and satellites such as Saturn{close_quote}s moon Titan. This reaction might further present a barrierless route to the formation of heteropolycyclic aromatic hydrocarbons via cyanobenzene in these extraterrestrial environments as well as hydrocarbon rich flames. {copyright} {ital 1999 American Institute of Physics.} thinsp

• OSTI ID: 698895
• Journal Information: Journal of Chemical Physics, Journal Name: Journal of Chemical Physics Journal Issue: 16 Vol. 111; ISSN JCPSA6; ISSN 0021-9606
• Country of Publication: United States
• Language: English

Related Subjects

40 CHEMISTRY
ANGULAR DISTRIBUTION
BENZENE
CARBON COMPOUNDS
CHEMICAL REACTIONS
CYANOGEN
DEUTERIUM COMPOUNDS
ISOTOPE EFFECTS
MOLECULAR BEAMS
MOLECULE-MOLECULE COLLISIONS
ORGANIC COMPOUNDS
RADICALS
TIME-OF-FLIGHT METHOD