Hirone Nakamura

Ion‐molecule reactions of N3+, N4+, O2+, and NO2+ in nitrogen containing traces of oxygen

A new sort of stationary pulsed afterglow method with a mass spectrometric analysis is presented to study quantitative ion behavior at atmospheric pressure. Repetitive x‐ray pulses from an electron linear accelerator are used to ionize gases. Experiments were carred out in a system of nitrogen containing traces of oxygen. The ion–molecule reaction rate constants for N3++O2 and N4++O2 were measured as (7.1±0.7)×10−11 and (2.86±0.3)×10−10 cm3 s−1, respectively. A main cause for ±10% errors in the rate constants is attributed to errors of measurements of oxygen contents. An error due to ion sampling through the reactor wall aperture is evaluated to be less than ±0.5%. Thus, the presented method is very useful for accurate quantitative study. Product ion NO+2 is shown to be lost in nitrogen via successive reaction. The endothermic reaction NO+2+N2→NO++N2O with a rate constant of 1.2×10−15 cm3 s−1 is postulated. The rate constant of the exothermic reaction O+2+N2→NO++NO was found to be less than 2×10−18 cm3 s−1.

Reactivity and structure of NO+2 produced by the N+3+O2 reaction

The experiments have been performed with a time‐resolved atmospheric pressure ionization mass spectrometer (TRAPI). The NO+2 ion produced by the reaction of N+3 with O2 was found to decay to NO+ by a unimolecular thermal decomposition reaction having a rate constant represented by 5.6×107 exp(−4500/RT) s−1. NO+2 was also found to react rapidly with C2H6 (k=8.7×10−10 cm3 s−1), although ONO+ being produced by the charge exchange between O+2 and NO2 (nitrogen dioxide) showed undetectable reactivity (k<2×10−12 cm3 s−1) at the same experimental conditions. It is concluded from the present results that NO+2 has not the usual structure of ONO+ but has a structure of NOO+. The initial product ion ratio of NO+2/NO+ in the N+3+O2 reaction was measured to be 1.72±0.2 at 303 K.

Pressure and temperature dependences of the ‘‘binary’’ ion–molecule reaction N+3+H2O→H2NO++N2

Experiments were carried out using a time‐resolved atmospheric pressure ionization mass‐spectrometer (TRAPI) in N2–H2O (∼1 ppm) system at temperatures from 233 to 543 K and at pressures from 167 to 760 Torr. The title reaction showed temperature and pressure dependences which were explained by the following scheme: N+3+H2O⇄(N+3⋅H2O)* (forward and backward rate constants ka and kb; (N+3⋅H2O)*→H2NO++N2 (forward rate constant kp; (N+3⋅H2O)* +N2→H2NO++2N2 (forward rate constant ka. Assuming that kd is equal to the collision rate constant of 7.1×10−10 cm3 s−1, the individual rate constants were determined as ka =2.8×10−9 cm3 s−1 (302 K), kb =17T3.6 s−1 where T is temperature in K, and kp =2.0×109 s−1 (302 K). The product H2NO+ ion changed by successive reactions with H2O into H2NO+⋅H2O and subsequently to H3O+.

Ions in carbon dioxide at an atmospheric pressure

Abstract The formation and decay of cluster ions, (CO 2 ) n + , (CO(CO 2 ) n ) + , H 2 O(CO 2 ) n ) + , (H(H 2 O)(CO 2 ) n ) + , and (H(H 2 O) 2 (CO 2 ) n ) + in atmospheric pressure carbon dioxide are observed with a time-resolved atmospheric pressure ionization mass spectrometer (TRAPI). It was found that the reaction of the cluster ions is not always analogous to that of the corresponding bare ions, and that a trace amount of impurities, i.e. H 2 O and CO, causes a decisive effect on the reaction course of cluster ions. Relevance of these observations is discussed to the radiolysis of carbon dioxide.

Core-core interaction potentials of alkali diatomic molecular ions

Abstract Core-core interaction potentials are calculated for Li + 2 , Na + 2 , K + 2 , Rb + 2 and Cs + 2 . The Thomas-Fermi-Dirac statistical model is employed to estimate the short range repulsive interaction potential. The attractive potential due to the core polarization is also estimated.

Recombination of N+4 and N+3 with electrons in atmospheric pressure nitrogen

Abstract Recombination rate constants of N + 4 + e − and N + 3 + e − in atmospheric pressure nitrogen at ambient temperature have been measured to be (4.6 ± 0.9) × 10 −6 and (3.7 ± 0.7) × 10 −6 cm 3 s −1 , respectively. Pressure dependence of these rate consta nts has been examined in a pressure range between 760 and 1315 Torr, and both decreased with the increase of pressure. The pressure dependence of rate constants was discussed in terms of the diffusion-controlled mechanism and two and three body mechanisms.

A study of Krypton encapsulation and adsorption in zeolite by means of neutron activation analysis

Abstract Encapsulation in zeolite is one of the promising methods of immobilization of radioactive 85Kr in waste management of nuclear fuel cycles. During our test studies of krypton encapsulation into zeolite and leakage from it, we have applied neutron activation analysis to determine the amounts of zeolite and krypton. This method has proved to be particularly preferable to the gravimetrical method when absorbed water can obscure the result of weight measurements. It has been shown that krypton can be encapsulated in both α- and β-cages, but that the krypton in the α-cage can be released easily at the expense of water absorption. Kr in the β-cage seems to be relatively stable. An explanation is given for this different behavior of krypton in α- and β-cages. It is also shown that there is another site for krypton, unstable and small in number, which we attribute to surface adsorption sites.

Measurement of the product ion ratio N4+/N3+ in the radiolysis of nitrogen

Abstract The ratio of N 4 + to N 3 + formed in the radiolysis of gaseous nitrogen has been measured to be 4.7 ± 0.4 using a time-resolved atmospheric pressure ionization mass spectrometer. The limit of error has been evaluated from the ion mass discrimination of the apparatus.

Comments on the ambipolar diffusion assumption in flowing-afterglow data analysis for positive-ion/molecule reactions

Abstract An ambipoIar diffusion assumption holds not for the reactant ions alone but for the sum of the reactant and product ions. With this point of view, a mathematical model of the data analysis to obtain rate constants for positive-ion/molecule reactions is presented. The model is applied to the reactions He+ + N2 → N2+ + He and N2+ + O2 → O2+ + N2. The solutions for these reactions are obtained with the aid of a computer for the flowing-afterglow conditions: average gas velocity, 8000 cm s−1; pressure, 0.400 torr; and temperature, 298 K. It is shown that conventional data analysis with the assumption of ambipolar diffusion of the reactant ions produces error both in the radial and axial directions. The error in rate constants due to this assumption amounts to several percent when the reaction length is 40 cm.

Ions in carbon dioxide at an atmospheric pressure—II. Effect of CO and O2 addition

Abstract The formation and the subsequent reactions of positive and negative ions were observed by a TRAPI in an atmospheric pressure carbon dioxide added with small amounts of carbon monoxide and oxygen. A relatively stable ion of (44 × n)+ (n ≥ 2) having a different reactivity from that of (CO2)+n was found to be one of major ionic species in this gas system. This species was tentatively assigned as [O2(CO)2]+ (CO2)n-2. A new reaction sequence of positive ions is proposed which can be operative in the radiolysis of carbon dioxide at 1 atm.