Thermal energy charge transfer

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... 

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. 

Mauclaire, G. Dera, D. Fenistein, S. Marx, R. Johnsen, R. Thermal energy charge transfer from He+ to O2 Kinetic energy, nature, and reactivity of the O product ions , J. Chem. Phys. 1979, 70,4023-4026. 

This transition is, at present, the shortest wavelength C.W. laser transition available and is widely used in the fields of photochemistry and photofabrication. Unfortunately, lasers pumped by Penning reactions are limited in output power by the saturation of the helium metastable density at high currents, exactly as in the case of the helium-neon system discussed,in section 11.4.2(d). In an attempt to overcome this limitation, considerable effort has been made to develop metal vapour laser systems excited by thermal-energy charge transfer. 

Thermal-energy charge transfer reactions. When the current in a helium discharge tube is increased from 100 mA to 10 A the density of helium ions, He, increases proportionally in contrast to the helium metastable density which... 

This process is known as thermal-energy charge transfer. 

Cadmium ion lasev transitions excited by thermal energy charge transfer reactions in a He-Cd discharge... 

At thermal energies, electron transfer is efficient even for highly exothermic (and thus far from resonant) reactions - in contrast with charge transfer at high energies, which is relatively inefficient at non-resonant conditions. For example, Xe+ charge transfer with NFIs (ionization potential of NH3 is 1.97 eV lower than that of Xe) is highly exothermic and occurs under thermal conditions of SIFT at around 52% of the collision rate, while with O2 it is nearly resonant AHt = —0.06 eV) but occurs only at around 2% of the collision rate (data from Anicich and ADO calculations ). 

Though thermally stable, rhodium ammines are light sensitive and irradiation of such a complex at the frequency of a ligand-field absorption band causes substitution reactions to occur (Figure 2.47) [97]. The charge-transfer transitions occur at much higher energy, so that redox reactions do not compete. 

By adding small amounts of H2 to the gas mixture and observing the rate of formation of ArH +, they also estimated the following overall rate constants for charge transfer at thermal ion energies. 

The pulsed source method, despite several limitations, appears to be a very useful technique for studying ion-molecule reactions at thermal energies. Although the studies to have date been limited primarily to simple hydrogen transfer reactions, the technique should also prove useful for studying charge transfer and hydride ion transfer reactions at thermal energies. 

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