Formation of NO(A 2Σ+, C 2Πr, D 2Σ+) by the ion–ion neutralization reaction between NO+ and C6F6− at thermal energy

Abstract

The ion–ion neutralization reaction between NO+ (X 1Σ+:v″=0) and C6F−6 has been spectroscopically studied in the flowing helium afterglow. In addition to the NO(A 2Σ+–X 2Πr) emission system, which has been found in the previous studies on the NO+/NO−2 and NO+/SF−6 reactions, the NO(C 2Πr–X 2Πr, D 2Σ+–X 2Πr) emission systems are observed in the NO+/C6F−6 reaction. The relative formation rates of NO(A), NO(C), and NO(D) are evaluated to be 1.0, 0.13±0.04, and 0.24±0.04, respectively. Only the v′=0 levels of NO(A,C,D) are formed, indicating that no energy is deposited into the vibration of NO(A,C,D). The rotational distributions of NO(A:v′=0), NO(C:v′=0), and NO(D:v′=0) are expressed by single Boltzmann rotational temperature of 500±50, 300±50, and 400±50 K, respectively. The average fractions of the total available energy deposited into rotation of NO(A), NO(C), and NO(D) are evaluated to be only 1.5±0.1%, 1.4±0.2%, and 1.9±0.2%, respectively. Most of all excess energy is expected to be partitioned into translation of the products. The observed vibrational and rotational distributions are less excited than statistical prior ones, indicating that the reaction dynamics is not governed by a simple statistical theory. The excitation mechanism of NO(A,C,D) in the NO+/C6F−6 reaction is compared with those in the NO+/NO−2 and NO+/SF−6 reactions, which give only the NO(A) state.