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])

• Published in: The Journal of chemical physics 1999-10, Vol.111:16
• Main Authors: Balucani, N., Asvany, O., Chang, A.H., Lin, S.H., Lee, Y.T., Kaiser, R.I., Bettinger, H.F., Schleyer, P.v., Schaefer, H.F. III
• Format: Article
• Language: English
• Subjects: ANGULAR DISTRIBUTION; AROMATICS; BEAMS; BENZENE; CARBON COMPOUNDS; CHEMICAL REACTIONS; COLLISIONS; CYANOGEN; DEUTERIUM COMPOUNDS; DISTRIBUTION; HYDROCARBONS; HYDROGEN COMPOUNDS; INORGANIC, ORGANIC, PHYSICAL AND ANALYTICAL CHEMISTRY; ISOTOPE EFFECTS; MOLECULAR BEAMS; MOLECULE COLLISIONS 400201 > Chemical & Physicochemical Properties; MOLECULE-MOLECULE COLLISIONS; ORGANIC COMPOUNDS; RADICALS; TIME-OF-FLIGHT METHOD
• ISSN: 0021-9606; 1089-7690
• DOI: 10.1063/1.480070

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 barri