The incorporation reaction of zinc(II) and cadmium(II) into 21-(4-nitrobenzyl)-5,10,15,20-tetrakis(4-sulfonatophenyl)-23H-porphyrin (NO2Bz(Htpps)4−; HP4−) and the dissociation reaction of the metalloporphyrins ([MP]3−) have been studied spectrophotometrically at I = 0.1 mol dm−3 (NaNO3). The formation rate of the metalloporphyrins is expressed by the following equation: d[MP3−]/dt = kfM[M2+][HP4−]+kfMOH[MOH+][HP4−]-kdMP[MP3−][H+]. The rate constants and the activation parameters of the reaction were found to be kfZn = (4.86 ± 0.06) × 102 mol−1 dm3 s−1 (25 °C), ΔH‡ = 62.1 ± 1.6 kJ mol−1, and ΔS‡ = 14.8 ± 5.3 J mol−1 K−1; kfZnOH = (6.39 ± 0.14) × 103 mol−1 dm3 s−1 (25 °C), ΔH‡ = 22.8 ± 0.9 kJ mol−1, and ΔS‡ = −90.2 ± 3.1 J mol−1 K−1; kdZnP = 122.3 ± 2.3 mol−1 dm3 s−1 (25 °C), ΔH‡ = 19.8 ± 2.2kJ mol−1, and ΔS‡ = −139 ± 18 J mol−1 K−1 for zinc(II) and kfCd = (1.17 ± 0.02) × 105 mol−1 dm3 s−1 (25 °C), ΔH‡ = 42.5 ± 1.3 kJ mol−1, and ΔS‡ = −5.3 ± 4.2 J mol−1 K−1; kdCdP = (2.51 ± 0.04) × 107 mol−1 dm3 s−1 (25 °C), ΔH‡ = 14.6 ± 0.5 kJ mol−1, and ΔS‡ = −54.3 ± 1.7 J mol−1 K−1 for cadmium(II). Nitrobenzyl group lowers the basicity of porphyrin. The effect of the lowered basicity appeared strongly in the following order for the formation rate and equilibrium constants of the metalloporphyrins: Cd2+ < Zn2+ < [ZnOH]+. A hydrogen-bond formation between [ZnOH]+ and the pyrrole proton in NO2Bz(Htpps)4− is proposed for the reaction based on the larger rate constant than the water-exchange rate constant enhanced by the hydroxide ion bound to zinc(II), the small activation enthalpy, the negative activation entropy, and the dependence of porphyrin basicity.

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.

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.

The formation process of Xe+* in the He afterglow reaction of Xe has been studied by observing Xe ii lines in the ultraviolet and visible regions. Sixty one Xe+* states in the 13.86–19.49 eV range were excited by the He(2 3S)+Xe+(5p5 2P03/2) excitation-transfer reaction. It was found that Xe+* was not formed by the He(2 3S)+Xe(6s 3P02) Penning type reaction and the He++Xe(6s 3P02) charge-transfer reaction. There were some unclassified Xe ii lines, which occupied 14% of the total production of Xe+*. Most of them were attributed to Xe+ transitions from unknown high energy Xe+* states in the 18–19.5 eV range. The electronic state distribution of individual Xe+* levels has been determined by taking account of radiative cascade for low lying electronic levels. The He(2 3S)+Xe+(2P03/2) reaction expressed no resonant character. The electronic state of Xe+* was distributed more widely than those of Ar+* and Kr+* in the He(2 3S)+Ar+(3p5 2P03/2), He(2 3S)+Kr+(4p5 2P01/2), and He(2 3S)+Kr+(4p5 2P03/2) reactions. The excitation mechanism of rare gas cations due to collisions between a rare gas metastable atom and a rare gas ion is discussed. The lack of the excitation processes of Kr+* and Xe+* by the He++Kr(3P02) and He++Xe(3P02) reactions was attributed to the absence of near-resonant Kr+(5p) and Xe+(6p) states whose excitation satisfies the selection rule of Δl=±1.

Articles you may be interested inRadiative charge transfer in He+ + H2 collisions in the milli-to nano-electron-volt range: A theoretical study within state-to-state and optical potential approaches J. Chem. Phys. 138, 104315 (2013); 10.1063/1.4793986Rovibrationally selected ion-molecule collision study using the molecular beam vacuum ultraviolet laser pulsed field ionization-photoion method: Charge transfer reaction of N2 +(X 2Σg +; v+ = 0-2; N + = 0-9) + ArThe NO ϩ (A 1 ⌸-X 1 ⌺ ϩ ) emission resulting from the He 2 ϩ /NO charge-transfer reaction at thermal energy has been observed in a He flowing afterglow. The vibrational and rotational distributions of NO ϩ (A) were determined from a spectral simulation. The average vibrational and rotational energies deposited into NO ϩ (A) were determined to be 0.22Ϯ0.02 and 0.10Ϯ0.1 eV, respectively. The vibrational population of NO ϩ (A) decreases rapidly for vЈϭ0 -2 and becomes flat for vЈ ϭ3,4, 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 type͒. The rotational distributions were expressed by single Boltzmann temperatures of 1170Ϯ100 K.