Thermal energy charge-transfer reactions

Hamilton C E, Bierbaum V M and Leone S R 1985 Product vibrational state distributions of thermal energy charge transfer reactions determined by laser-induced fluorescence in a flowing afterglow Ar" + CC -> CC (v= 0-6) + Ar J. Chem. Rhys. 83 2284-92... 

Selected Cross Section and/or Rate Constants for Charge-transfer Reactions of He+ and He at Thermal Energies... 

WITH 18 Neutral Reactants at Thermal Energies, and also the Ionization Energies of the Reactants, the Thermal Capture Rate Constants k, and the Exoergicity for the Respective Charge-Transfer Reactions Using the Adiabatic RE(KrJ) = 12.85 eV... 

Metastable oxygen ions 02(a ITu) react fast with atoms or molecules (Ar, N2, CO, H2) in reactions that are endothermic with ground-state oxygen ions the respective rate constants do not depend much on translational energy. An interesting case is the charge-transfer reaction of electronically excited NO+(a S" ) with Ar The reaction is endothermic by 0.09 eV, and its rate constant increases with translational energy from the thermal value of 3 x 10 " cm s to a value of about 9 x 10 cm s at 3 eV in a way typical of... 

Several negative-ion-neutral reactions have been studied, principally in an attempt to determine limits for the electron affinities of important diatomic and triatomic molecules. In the more widely used method, one looks for charge transfer between a low-energy (preferably thermal), negative ion X and the neutral molecule Y. Alternatively, the kinetic energy threshold for an endothermic charge transfer reaction between X and Y is measured. 

The major application of this technique, principally by Lindholm and co-workers (see Chapter 10), has capitalized on the above limitation in a study of charge-transfer processes, where the products may exhibit a thermal energy distribution. Even in this application, cross sections are difficult to obtain because the sampling volume is not well defined. Lindholm has been careful to quote only Q values which are estimates of the relative reaction efficiencies. There is another reason why any such cross section so measured may be unreliable. It is plausible, and indeed it has recently been demonstrated, that charge-transfer reactions may yield some products which are forward-scattered in the laboratory framework these would result from collisions with small impact parameters. To the extent that these products will not be detected in a transverse tandem machine, the measured cross section will be underestimated. 

P. Warneck, Studies of ion-neutral reactions by a photoionization mass-spectrometer technique. II. Charge-transfer reactions of argon ions at near-thermal energies, J. Chem. Phys. 46,513-519(1967). 

F. A. Wolf and B. R. Turner, Energy dependence of charge-transfer reactions in the thermal and low-electron-volt region, J. Chem. Phys. 48, 4226-4233 (1968). 

Thermal energy charge transfer reactions with several cations (Ar+, CO", COJ, Kr" ) yielding PHJ were observed with the double resonance technique. Product distribution and rate constants (not for Kr+) were measured (see p. 217) [18]. PHJ from the ion-molecule reaction PH3 + PH" PHJ + PH2 had been earlier observed by ICR [16]. 

More recently, methods based on laser preparation of reagent ions and laser-based detection of product ions have been accomplished for the thermal energy charge transfer reaction DBr+ + HBr HBr+ + DBr. REMPI was used to prepare DBr+ in specific vibrational and spin-orbit states, and the HBr+ product state was measured by laser-induced fluorescence. The largest rate constants were observed for near-resonant processes in which both the vibrational and the spin-orbit quantum numbers remained unchanged. 

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