Transfer of F− in the reaction of SF 6 − with SOF4: Implications for SOF4 production in corona discharges

The temperature (T) and electric field-to-gas pressure (E/P) dependences of the rate coefficientk for the reaction SF ₆ ^– +SOF₄SOF ₅ ^– +SF₅ have been measured. ForT<270 K,k approaches a constant of 2.1×10^–9 cm³/s, and for 433>T>270 K,k decreases withT according tok (cm³/s)=0.124 exp [–3.3 lnT(K)]. ForE/Pk has a constant value of about 2.5×10^–10 cm³/s, and for 130 V/cm·torr>E/P>60 V/cm·torr, the rate is approximately given byk (cm³/s)7.0×10^–10 exp (–0.022E/P). The measured rate coefficient is used to estimate the influence of this reaction on SOF₄ production from negative, point-plane, glow-type corona discharges in gas mixtures containing SF₆ and at least trace amounts of O₂ and H₂O. A chemical kinetics model of the ion-drift region in the discharge gap is used to fit experimental data on SOF₄ yields assuming that the SF ₆ ^– +SOF₄ reaction is the predominant SOF₄ loss mechanism. It is found that the contribution of this reaction to SOF₄ destruction falls considerably below the estimated maximum effect assuming that SF ₆ ^– is the predominant charge carrier which reacts only with SOF₄. The results of this analysis suggest that SF ₆ ^– is efficiently deactivated by other reactions, and the influence of SF ₆ ^– +SOF₄ on SOF₄ production is not necessarily more significant than that of other slower secondary processes such as gas-phase hydrolysis.     

Pulsed Electron-Beam Ionization of Humid Air and Humid Air/Toluene Mixtures: Time-Resolved Cationic Kinetics and Comparisons with Predictive Models

The technique of pulsed electron-beam high-pressure mass spectrometry wasused to investigate the sequential cationic chemistry in humid air streamsat 4.2×10² Pa and 380 K. The system was then modeled usingthe ACUCHEM program, incorporating thirty-five reactions taken from theformulations given in Part I of the new National Institute of Standards andTechnology (NIST) Chemical Kinetics Database for Humid Air Plasmas. Theresulting temporal ion profiles were found to be in qualitative agreementwith the laboratory data. Analogous pulsed electron-beam measurements werealso carried out with humid air samples containing low levels of toluene,and these results were also reproduced qualitatively by a model incorporatingforty-eight reactions after the inclusion of an unexpected, but crucial,channel involving the reaction of an intermediate air-generated cluster ionwith toluene. The benefits of laboratory validation of predictive databasesin systems for which the literature data are incomplete are emphasized.     

High-pressure photoionization mass spectrometry. Effect of internal energy and density on the ion–molecule reactions occurring in methyl,dimethyl, and trimethylamine

The ion–molecule reactions of CH₃NH₂⁺, (CH₃)₂NH⁺, and (CH₃)₃N⁺ with the respective amines have been investigated at thermal kinetic energies in a high-pressure photoionization mass spectrometer at several wavelengths (energies) in the vacuum ultraviolet. The absolute rate coefficient for proton transfer from (CH₃)₃N⁺ to (CH₃)₃N decreases from 8.2 × 10^?10 cm³/molecule · sec at 147.0 nm (8.4 eV) to 4.9 × 10^?10 cm³/molecule. sec at 106.7-104.8 nm (11.7 eV). In dimethylamine, the rate coefficient decreases from 11.6 × 10^?10 cm³/molecular. sec at 8 4 eV to 10.2 × 10^?10 cm³/molecule osec at 11.7 eV, while no significant effect of energy was detected in methylamine. The reactions of several fragment ions are also reported. Experiments were also carried out at pressures up to 0.5 torr in order to investigate the further solvation of CH₃NH₂⁺, (CH₃)₂NH₂⁺, and (CH₃)₃NH⁺. It was found that the maximum proton solvation numbers in methyl-, dimethyl-, and trimethyl-amine are 4, 3, and 2, respectively, under these conditions.     

Formation of association ions in the photoionization of alkyl halides

The methyl and ethyl chlorides and bromides, as well as methyl iodide, were photoionized in the vacuum ultraviolet at 300 K in a mass spectrometer over the pressure range 0.5 to approximately 100 millitorr. Under these conditions, stabilized parent ion dimers are found in CH₃Br, CH₃I, and C₂H₅Br, but not in the chlorides. Lower limits for the dissociative lifetimes of the ion–molecule collision complexes were estimated and are as follows: (CH₃Br)₂⁺, 1.6 μs; (CH₃I)₂⁺, 1.9 μs; and (C₂H₅Br)₂⁺, 5.4 μs. An increase in photon energy (internal energy content of the reactant ion) decreases the dissociative lifetime of the collision complex in CH₃I.     

Argon sensitized formation of Xe+2: A new mechanism for the Jesse effect

Photoexcitation of the argon resonance states in the presence of xenon leads to Xe⁺₂. Kinetic analysis indicates rapid near-resonant energy transfer between argon and xenon atoms. The possibility of an analogous mechanism in other rare gas systems is examined.