Shingo Matsuoka

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.

STUDY ON THE BEHAVIOR OF RADIOLYTICALLY PRODUCED HYDROGEN IN A HIGH-LEVEL LIQUID WASTE TANK OF A REPROCESSING PLANT: HYDROGEN CONSUMPTION REACTION CATALYZED BY Pd IONS IN THE SIMULATED SOLUTION

Abstract It is well known that not all of the hydrogen formed in high-level liquid waste comes out in the gas phase because hydrogen is consumed by some unclarified secondary reaction. Using a simulated waste solution, it was found that the H2 consumption reaction is not caused by radiation as was thought but is caused by a catalytic effect of Pd ions, which suggests that the same reaction proceeds in actual solution. Using the catalytic reaction rate constant measured in the simulated solution, the analysis showed that the H2 concentration in the gas phase does not reach its explosion limit of 4% even if the sweeping air stops for a long time.

Effect of water on the radiolysis of carbon dioxide

Abstract Water was found to accelerate the back reaction of CO 2 radiolysis. Concentration of carbon monoxide reached only a low level( 2 ) by the radiolysis of wet carbon dioxide, while it reached much higher (>250 ppm in CO 2 ) by that of dry carbon dioxide. Clustered ions, O 2 ± (H 2 O) m (CO 2 ) n , are considered for the ixidizing species responsible for the back reaction.

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.

Development of NOx Recycle Process for Practical Use at Reprocessing Plant

To realize the NOx recycle process using the vacuum pressure swing adsorption method reported previously, development experiments were carried out. Among such experiments were the removal of volatile ruthenium tetroxide from the off-gas, 23-month operation of a bench-scale apparatus and 100-day operation of a pilot plant ⅕ the size of the actual scale. After evaluation of the results for operability and durability of components under acidic conditions, this process was concluded applicable to an actual plant. Compared to the conventional NOx production method using chemical reaction, it has the great advantage of reducing largely low-level radioactive and non-radioactive sodium nitrate waste. With this conclusion, the procedure to install the process at the Rokkasho Reprocessing Plant has been commenced.

Space-charge effects in flowing-afterglow data analysis for negative-ion/molecule reactions

Abstract In positive-ion/negative-ion plasmas, the space-charge fields (ambipolar fields) in the flow tube vary as the ion/molecule reaction proceeds if the value of the diffusion coefficient of the product ions is not equal to that for the reactant ions. The variation of the fields, however, has not been incorporated in conventional flowing-afterglow data analysis. In this report a mathematical model of the data analysis with a variable-field term is presented for negative-ion/molecule reactions, as examples of reactions in ion/ion plasmas. The model is applied to the reactions F − + CH 3 Br → Br − + CH 3 F and Cl − + CH 3 Br → Br − + CH 3 Cl, and then the errors in the rate constants arising from neglecting the variation of the fields are evaluated with the aid of a computer for the flowing-afterglow conditions: average velocity of helium buffer gas, 8000 cm s −1 ; pressure, 0.40 Torr; and temperature, 298 K. The magnitude of the error depends on the extent of the inequality of the diffusion coefficients between the reactant and the product ions, on the reaction length, and on the extent of progress of the reaction. For the F − + CH 3 Br reaction, the error amounts to 15–30% when the reaction length is 70 cm.