The Influence of Vibrational Excitation of NO+(X1Σ+ : v″) on the Formation of NO* by the NO+ + C6F6− Neutralization Reaction at Thermal Energy

Abstract

Abstract The NO(A2Σ+-X2Πr, C2Πr-X2Πr, D2Σ+-X2Πr) emissions resulting from the mutual ion–ion neutralization reaction between NO+(X1Σ+) and C6F6− have been measured at various source gas pressures of NO+ in a flowing afterglow in order to examine the influence of vibrational excitation in NO+(X : v″). N2O was used as a source gas of NO+(X). The NO(A-X, C-X, D-X) emissions from only the v′ = 0 level were observed at high N2O pressures above ca. 60 mTorr (1 Torr = 133.322 Pa), where only NO+(X : v″ = 0) was present. On the other hand, the NO(A-X) emission from v′ = 1, 2 and the NO(D-X) emission from v′ = 1 appeared at low N2O pressures below ca. 60 mTorr, where NO+(X : v″ > 0) was present. It was found that vibrational excitation in NO+(X : v″) results in vibrational excitation of the product NO(A, D : v′ = v″) molecule because of favorable Franck–Condon factors for the NO+(X : v″) → NO(A, D : v′ = v″) neutralization. The fact that the vibrational excitation of NO(D) is slightly higher than that of NO(A) indicated that the relative coupling strength between NO+(X : v″ > 0) + C6F6− and NO(D : v′ = v″) + C6F6 to that between NO+(X : v″ = 0) + C6F6− and NO(D : v′ = 0) + C6F6 is larger than that in the corresponding processes leading to NO(A : v′ = v″). The lack of vibrational excitation of NO(C) was explained by the predissociation of NO(C : v′ > 0).