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

Abstract

C₂(a ³Π_u) 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 ³Π_u) by NO is determined both from laser induced fluorescence of C₂(a ³Π_u) 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 ³Π_u)+NO→CN(B ²Σ⁺ or A ²Π)+CO(X ¹Σ⁺). Quenching rate coefficients of C₂(a ³Π_u) by vinyl cyanide and ethylene are also reported.