Asymmetric Charge Transfer Research Articles

Low Energy Ion-Netural Reactions. III. Ar++NO, Kr++NO, Ar++O2, Kr++O2 and Ar++CO

Molecular asymmetric charge transfer reactions in the systems Ar + –No, Kr + –NO, Ar + –O 2 , Kr + –O 2 and Ar + –CO were studied by an injected-ion drift tube technique in the energy range from 0.04 eV to 3 eV. All reactions have large cross sections in spite of the large exothermicities, and each of them has a minimum. The cross sections in the low energy part have E -1/2 dependence when the reactant is NO, while they have E -1 dependences when the reactant is O 2 or CO. An hypothesis is proposed to explain the large cross sections, but without quantitative treatment.

Molecular charge transfer reactions of monosubstituted benzenes at low energies

Cross sections for the symmetrical and exoergic asymmetrical charge transfer reactions of a series of monosubstituted benzenes were measured for primary-ion kinetic energies between 30 and 150 eV. In this energy range, the charge transfer cross sections of all the reactions were found to be larger than the gas-kinetic collisional cross sections, and their velocity dependence typical of resonant processes. These features seem to indicate that transitions to excited levels occur with high probability. The momentum transfer and the conversion of translational to internal energy in all the reactions was low, as expected for reactions having large impact parameters. In contrast to atomic and diatomic systems, no systematic difference was observed between symmetrical and asymmetrical processes, and molecular parameters other than the ionization potential of the system were found to affect the cross section. For a given projectile ion the cross section increased with the polarizability of the target molecule. This increase is associated with the deformation and lowering of the potential barrier. The nature of the projectile ion affected the magnitude of the cross section to about the same extent as did the target molecule, and this seems to be related to the energy defect of the reaction and to the dimensions and complexity of the projectile ion.

Low energy study of symmetric and asymmetric charge-transfer reactions

A modified Varian ion cyclotron resonance (ICR) mass spectrometer was used to measure absolute rate constants for charge transfer from Kr+ to Kr and CO as well as from CO+ to Kr and CO. The technique of double resonance permitted measurement of the rate constants over the translational energy range from 0.1 to 10 eV. Ion motion in an ICR mass spectrometer was analyzed to give an average ion velocity which was used to convert the reaction rate constants to cross sections. These results are compared to the theoretical results of Rapp and Francis, with Langevin and with existing experimental results. One of the most striking results is that at a very low energy the cross sections for the crossed or asymmetric reactions are substantially greater than the cross sections for the symmetric charge-transfer reactions.

Effect of Long-Range Forces in Near-Resonant Charge Transfer: Application toHe++ K, Rb, and Cs

Near-resonant charge transfer in asymmetric collisions is often dominated by long-range forces due to polarization and sometimes to ion-quadrupole interactions. These interactions can lead to regions of strong coupling at large distances. The parameters necessary for estimating the cross sections by a modified Demkov formula (for strong coupling without crossing) can be obtained from a knowledge of simple atomic properties such as ionization potentials and polarizabilities. These formulas are applied to the calculation of the cross sections for the ${\mathrm{He}}^{+}$ + K, Rb, and Cs asymmetric charge-transfer reactions and are compared with the experimental measurements of Peterson and Lorents. For these systems several inelastic channels are open and the theory predicts the relative abundances of the various excited states of He (n=2).

Asymmetric charge transfer reactions of rage gas ions at low ion energies

The charge transfer reactions of Kr +, Ar + and Ne + ions with a number of polyatomic molecules have been studied at ion energies less than 1 eV. Charge transfer mass spectra and total rate coefficients for charge transfer have been measured. In no case studied does the measured rate coefficient exceed that calculated for an orbiting collision based on the ion-induced dipole model.

Resonance charge transfer between protons and excited hydrogen atoms. III. Quantal eight-state approximation

Cross sections for symmetrical resonance and asymmetrical resonance charge transfer occurring between protons and hydrogen atoms in the second quantum level have been calculated in the quantal two-state and eight-state approximations using the impact parameter formulation. Momentum transfer has been taken into account by the method suggested by Cheshire (1967). As one goes from the quantal two-state approximation to the eight-state approximation, there is a considerable change in the results, especially at low energies of impact. The cross sections obtained by the quantal eight state approximation and those obtained by Bates and Reid (1969) using a classical approximation are in remarkably close accord.

Note on near-infrared operating characteristics of the mercury ion laser

Additional excitation mechanisms, apparently overlooked in [1], but previously reported to be responsible for the selective excitation of the Hg II 7p 2 P_{3/2} upper state of the 6150-A laser line in mercury-helium lasers, are referenced and discussed. It is pointed out that asymmetric charge transfer and Penning-type ionization reactions can also account for the selective excitation of the Hg II 7p 2 P_{3/2} state as well as direct electron impact excitation from the Hg I ground state.

Flowing Afterglow Studies of the Reactions of the Rare-Gas Molecular Ions He2+, Ne2+, and Ar2+ with Molecules and Rare-Gas Atoms

The flowing afterglow technique has been used to measure rate coefficients and product channels for the reactions of He2+, Ne2+, and Ar2+ with the rare-gas atoms Ne, Ar, and Kr, and with the molecules NO, O2, CO, N2, and CO2 at 200°K. These reactions are found to proceed principally by asymmetric charge transfer. The experimental results for the reactions of the rare-gas molecular ions with rare-gas atoms indicate a correlation between reaction probability and reaction exoergicity analogous to that observed for asymmetric atomic ion–atomic neutral charge-transfer reactions. The reactions with molecules are found to proceed with unit reaction probability with the exception of the reactions Ar2++O2 and Ar2++NO. The reaction probability for the reactions of the molecular rare-gas ions with molecules is not very sensitive to an energy resonance criterion. Finally, rate coefficients and reaction channels for the reaction of the mixed rare-gas molecular ions HeNe+, ArKr+, and ArCO+ with Ne, Kr, and CO, respectively, are reported.

Oscillatory Structure in Total-Charge-Transfer Cross Sections

Oscillatory structure has been observed in total symmetric and asymmetric charge-transfer cross-section measurements involving the alkali-metal atoms. Cross sections with oscillations similar to experimental results had been obtained from impact-parameter calculations using a two-state approximation with an interaction potential difference containing a maximum. This paper describes a physical model of charge transfer relating to the oscillatory electron capture probability. The ${\mathrm{Li}}^{+}$ + Li calculations of Peek et al. are examined and used as an example to relate capture-probability oscillations to those in total cross section. Computed capture probabilities having anomalous oscillations are shown as a function of impact parameter at several velocities. The capture-probability maxima are shown as contours on a plot of impact parameter versus inverse impact velocity. This plot illustrates capture-probability oscillations having a nearly stationary phase over a range of impact parameters, which results in oscillations in the total cross section. Oscillation damping and phase-constant effects are briefly examined to relate experimental results with theory. Near-resonant asymmetric oscillations are also discussed.

Ionization Cross Sections for Neutral—Neutral Collisions Utilizing Asymmetric Charge Transfer

Ionization cross sections for low energy collisions of neutral nitrogen molecules or neutral argon atoms, using asymmetric charge transfer

Calculations of atomic asymmetric charge transfer

Tables are presented from which the cross sections for asymmetric atomic charge transfer may be calculated, using a two-state approximation after the method of Rapp and Francis. A relation similar to the adiabatic maximum rule is derived with the elimination of the empirical `adiabatic parameter'.

Exact numerical solution for asymmetric charge transfer

Exact numerical solution for asymmetric charge transfer