Hiroaki Ishimi

Formation of NO(A 2Σ+) by the neutralization reaction between NO+ and SF−6 at thermal energy

An optical spectroscopic study has been made of the ion–ion neutralization reaction between NO+(X 1Σ+:v‘=0) and SF−6 in the flowing afterglow. Only the NO(A 2Σ+–X 2Πr) emission from v’=0 was excited, indicating that no energy is deposited into the vibration of NO(A). The rotational distribution of NO(A:v’=0) was expressed by a single Boltzmann rotational temperature of 600±50 K. The average fraction of the total available energy deposited into rotation of NO(A) was evaluated to be only 1.9%. Most of all excess energy was expected to be partitioned into translation of the products due to a strong mutual Coulombic attractive force between NO+ and SF−6. The observed vibrational and rotational distributions were less excited than statistical prior ones, indicating that the reaction dynamics is not governed by a simple statistical theory. The mechanism of the selective excitation of NO(A) in the ion–ion neutralization reaction was discussed.

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

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 tra...

Nascent rovibrational distribution of NO+(A 1Π) produced from charge-transfer reaction of He2+ with NO at thermal energy

The NO+(A 1Π-X 1Σ+) emission resulting from the He2+/NO charge-transfer reaction at thermal energy has been observed in a He flowing afterglow. The vibrational and rotational distributions of NO+(A) were determined from a spectral simulation. The average vibrational and rotational energies deposited into NO+(A) were determined to be 0.22±0.02 and 0.10±0.1 eV, respectively. The vibrational population of NO+(A) decreases rapidly for v′=0–2 and becomes flat for v′=3,4, indicating that the vibrational distribution is bimodal. The bimodal vibrational distribution was explained as due to either two different entrance channels or two different dynamics (Demkov or Landau–Zener type). The rotational distributions were expressed by single Boltzmann temperatures of 1170±100 K.

Electronic excitation of NO by the ion/ion neutralization reaction between NO+ and C6F5CF3− at thermal energy

Abstract The ion/ion neutralization reaction between NO+(X1Σ+: v″ = 0) and C6F5CF3− has been spectroscopically studied in the flowing helium afterglow. The NO(A2Σ+-X2IIr, C2IIr-X2IIr, D2Σ+-X2IIr) emission systems are observed in the NO+/C6F5CF3− reaction, as in the NO+/C6F6− reaction reported previously. The same electronic state selectivity between the NO+/C6F5CF3− and NO+/C6F6− reactions suggests that the molecular symmetry of the negative ion is insignificant for the electronic state selectivity in the ion/ion neutralization reaction. The relative formation rates of NO(A), NO(C), and NO(D) in the NO+/C6F5CF3− reaction are evaluated to be 1.0, 0.41 ± 0.003, 0.060 ± 0.010, 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 temperatures of 500 ± 50 K, 300 ± 50 K 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 1.8 ± 0.2%, 1.4 ± 0.2%, and 2.5 ± 0.3%, respectively. The observed vibrational and rotational distributions are compared with statistical prior ones in order to obtain information on the dynamical feature of the reaction.

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

The ion–ion neutralization reactions of NO+(X 1Σ+:v″=0) with C6F5Cl−, C6F5Br−, and C6F−5 have been spectroscopically studied in the flowing helium afterglow. The NO(A 2Σ+– X 2Πr,C 2Πr–X 2Πr,D 2Σ+–X 2Πr ) emission systems are observed in the NO+/C6F5Cl− reaction with the branching ratios of 0.96, 0.017, and 0.028, respectively, while only the NO(A–X) emission system is found in the NO+/C6F5Br− and NO+/C6F−5 reactions. The vibrational and rotational distributions of NO(A,C,D) indicate that only 1%–11% of the excess energy is deposited into vibration and rotation of NO(A,C,D) for all the reactions. In the NO+/C6F5X− (X=Cl,Br) reactions, a major part of the excess energy is expected to be partitioned into the relative translational energy of the neutral products and the vibrational energy of C6F5X. A comparison of the observed vibrational and rotational distributions with the statistical prior ones indicates that the reaction dynamics is not governed by a simple statistical theory because of the large impact ...

Emission spectra of HeAr2+ and HeKr2+ heterotrimer ions produced in a helium flowing afterglow

Abstract Emission spectra resulting from clustering reactions of He + with a heavier rare gas Rg(Rg=Ne, Ar, or Kr) have been studied in a helium flowing afterglow at various stagnation pressures of Rg. At low stagnation pressures, emission spectra of HeRg + heterodimer ions were found for Rg=Ne, Ar, and Kr due to radiative association and three-body clustering reactions. At high stagnation pressures, new continuous bands were found for Rg=Ar and Kr at longer-wavelength region of the heterodimer bands. They were attributed to bound-free transitions of HeRg 2 + heterotrimer ions. The HeRg 2 + bands consisted of two components: the first continuum degraded to the red from near the HeRg + (B  2 Σ + –X  2 Σ + ) transition, and the second continuum, a roughly Gaussian feature at longer wavelengths. The first and second components were ascribed to the B 1/2–X 1/2 and B 1/2–A 2  1/2 transitions of HeRg 2 + , respectively. The emission intensity of the second continuum increased more rapidly than that of the first one with increasing the stagnation pressure of Rg or a foreign gas. It was explained by the fact that the second continuum arises dominantly from low vibrationally excited levels formed by collisional relaxation of the upper vibrational levels of HeRg 2 + (B 1/2). The geometries of HeRg 2 + in the upper B 1/2 state and the lower X 1/2 and A 2  1/2 states were attributed to Rg⋯He + Rg and Rg⋯HeRg + , respectively, and the bound-free character derives from attractive Rg⋯He + and repulsive Rg⋯He bonds in Rg⋯(HeRg) + .