The kinetics of free radicals generated by IR laser photolysis. I. Reactions of C2(a 3Πu) with NO, vinyl cyanide, and ethylene

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Abstract
C2(a 3Πu) molecules are produced by multiple photon dissociation of either vinyl cyanide or ethylene with the focused output from a CO2 TEA laser. Their reaction with NO is reported in this paper. The total quenching rate coefficient of C2(a 3Πu) by NO is determined both from laser induced fluorescence of C2(a 3Πu) and from the time resolved chemiluminescence from CN(B 2Σ+) and CN(A 2Π) which are formed in the reaction, and is (7.5±0.3)10−11 cm3 molecule−1 sec−1. The vibrational energy disposal within the B 2Σ+ and A 2Π states of CN is estimated from the resolved bands of the CN(B 2Σ+→X 2Σ+) and CN(A 2Π→X 2Σ+) emission systems. Vibrational levels of CN(B 2Σ+) up to at least v′=5 but lower than v′=10 are excited, accompanied by high rotational excitation. CN in the A 2Π state is excited to at least the 16th vibrational level. The reaction populates the A 2Π state about 7 times more efficiently than it does the B 2Σ+ state. The reaction mechanism is discussed, and it is concluded that most of the electronically excited molecules are produced via the single step reaction C2(a 3Πu)+NO→CN(B 2Σ+ or A 2Π)+CO(X 1Σ+). Quenching rate coefficients of C2(a 3Πu) by vinyl cyanide and ethylene are also reported.