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.

Formation of NO(A 2Σ+,C 2Πr,D 2Σ+) by the ion–ion neutralization reactions of NO+ with C6F5Cl−, C6F5Br−, and C6F−5 at thermal energy

“…14,15 In brief, the metastable He(2 3 S) atoms and He ϩ and He 2 ϩ ions were generated by a microwave discharge of the high purity He gas in a discharge flow operated at 0.5-1.5 Torr ͑1 Torrϭ133.3 Pa͒. All experiments were carried out by removing the He ϩ and He 2 ϩ ions by using a pair of ion-collector grids placed between the discharge section and the reaction zone.…”

“…These values were obtained assuming that the C→A and D→A radiative-cascade processes are negligible for the formation of NO(A). 14,15 The relative formation rates of NO(A,C,D) were unchanged in the He pressure range 0.5-1.5 Torr, leading us to conclude that the electronic quenching of NO(A,C,D) by collisions with the buffer He gas is insignificant during short radiative lifetimes of ϭ͑192-202͒Ϯ14 ns for NO(A 2 ⌺ ϩ :vЈϭ0,1), 20 р2.7 Ϯ1.5 ns for NO(C 2 ⌸ r :vЈϭ0), 28 and 16.1Ϯ0.7 ns for NO(D 2 ⌺ ϩ :vЈϭ0). 28 The relative formation rates of NO(C,D) decrease with increasing mass of halogen atom substituted to the C 6 F 5 group and they become zero for the case of the heaviest C 6 F 5 Br Ϫ ion.…”

“…The simulation method was the same as that reported previously. 14,15 As a representative result, the observed NO(A -X) spectrum in the NO ϩ /C 6 F 5 Cl Ϫ reaction is compared with the best fit one ͑Fig. 5͒.…”

“…The NO ϩ -C 6 F 5 X Ϫ ͑XϭCl,Br͒ and NO ϩ -C 6 F 5 Ϫ separations at crossing points R c are calculated using the same relation as that reported previously. 14,15 In the calculations, the following electron affinities were used: C 6 F 5 Cl ͑0.48 eV͒, 33 C 6 F 5 Br ͑0.47 eV͒, 33 and C 6 F 5 ͑3.4 eV͒. 34 The R c values for each reaction are given in Table VI. The ion-ion neutralization reactions proceed through an approach of the NO ϩ (X 1 ⌺ ϩ ) and C 6 F 5 X Ϫ or C 6 F 5 Ϫ ion pair under their mutual Coulombic field followed by an electron transfer from C 6 F 5 X Ϫ or C 6 F 5 Ϫ to NO ϩ .…”

“…We have recently investigated the excitation processes of NO by ion-ion neutralization reactions of NO ϩ with such negative ions as SF 6 Ϫ , C 6 F 6 Ϫ , and C 6 F 5 CF 3 Ϫ by using the flowing-afterglow method [14][15][16][17] NO ϩ ͑ X 1 ⌺ ϩ ͒ϩSF 6 Ϫ ͑2͒ →NO͑A 2 ⌺ ϩ :vЈϭ0 ͒ϩSF 6 , NO ϩ ͑ X 1 ⌺ ϩ ͒ϩC 6 F 6 Ϫ ͑3͒ →NO͑A 2 ⌺ ϩ ,C 2 ⌸ r ,D 2 ⌺ ϩ :vЈϭ0 ͒ϩC 6 F 6 , NO ϩ ͑ X 1 ⌺ ϩ ͒ϩC 6 F 5 CF 3 Ϫ →NO͑A 2 ⌺ ϩ ,C 2 ⌸ r ,D 2 ⌺ ϩ :vЈϭ0 ͒ϩC 6 F 5 CF 3 . ͑4͒…”