Differential Cross Sections For Charge Transfer Research Articles

Single- and double-charge transfer in slow He2+–He collisions

The single- and double-electron capture processes in He2+–He collisions are investigated by the fully quantum-mechanical molecular orbital close-coupling method employing a basis containing 15 gerade and 14 ungerade molecular states. The energies and wavefunctions of He22+ molecular states included in the study are determined ab initio by the multireference single- and double-excitation configuration interaction method. The dominant capture mechanisms are discussed and the integral and differential charge transfer cross sections are calculated in the energy range of 0.0005–17.5 keV/u and compared with other available experimental and theoretical results.

Differential charge-transfer cross sections for systems with energetically degenerate or near-degenerate channels

Resolution plays a vital role in spectroscopic studies. In the usual recoil-ion momentum spectroscopy (RIMS), Q-value resolution is relied upon to distinguish between different collision channels: The better the Q-value resolution, the better one is able to resolve energetically similar channels. Although traditional COLTRIMS greatly improves Q-value resolution by cooling the target and thus greatly reducing the initial target momentum spread, the resolution of the technique is still limited by target temperature. However, with the recent development in RIMS, namely, magneto-optical trap recoil ion momentum spectroscopy (MOTRIMS) superior recoil ion momentum resolution as well as charge transfer measurements with laser excited targets have become possible. Through MOTRIMS, methods for the measurements of target excited state fraction and kinematically complete relative charge transfer cross sections have been developed, even for some systems having energetically degenerate or nearly degenerate channels. In the present work, the systems of interest having energy degeneracies or near degeneracies are ${\mathrm{Rb}}^{+}$, ${\mathrm{K}}^{+}$, and ${\mathrm{Li}}^{+}$ colliding with trapped $\mathrm{Rb}(5l)$, where $l=s$ and $p$.

Absolute differential and integral cross sections for charge transfer of keV O+ ions with CO2

We report measurements of the absolute differential cross sections for charge-transfer scattering of 0.5, 0.85, 1.5, 2.8 and 5 keV O+ ions by CO2 at scattering angles between 0.04° and 2.9° in the laboratory frame. Cross sections for both O+(4S) ground-state and O+(2D, 2P) metastable ions are presented. The angular dependence of the differential cross sections is similar for both ground-state and metastable ions but the ground-state integral cross section is greater than that for metastable ions over most of the energy range considered.

Charge transfer of 0.5-, 1.5-, and 5-keV protons withH2O:mAbsolute differential and integral cross sections

We report measurements of the absolute differential cross sections for charge-transfer scattering of 0.5-, 1.5-, and 5-keV protons by H{sub 2}O at laboratory scattering angles between 0.01{degree} and 2.6{degree}. Absolute integral cross sections are also reported and compared to the published total cross sections. {copyright} {ital 1997} {ital The American Physical Society}

Charge transfer of 0.5-, 1.5-, and 5-keV protons with atomic oxygen: Absolute differential and integral cross sections.

We report measurements of the absolute differential cross sections for charge-transfer scattering of 0.5-, 1.5-, and 5-keV protons by atomic oxygen at scattering angles between 0.01\ifmmode^\circ\else\textdegree\fi{} and 2.6\ifmmode^\circ\else\textdegree\fi{} in the laboratory frame. Absolute integral cross sections are also reported and compared with previously published total cross sections. The measurements were made using a flowing gas target, which consisted of a mixture of atomic and molecular oxygen produced by passage of ${\mathrm{O}}_{2}$ through a microwave discharge. The cross sections for atomic oxygen were obtained by appropriate subtraction of the signal due to molecular oxygen from that due to the mixture of O and ${\mathrm{O}}_{2}$. \textcopyright{} 1996 The American Physical Society.

Molecular calculation of total and differential charge transfer cross sections in C4++He collisions

Total and differential cross sections are calculated for single and double charge transfer in C4++He collisions, for the range of impact energies 0.04<E<6 keV amu-1. An overall good agreement is obtained with published data, with some exceptions that are analysed. New partial cross sections for single and double electron capture into the most relevant atomic channels are also reported and are of predictive value. Transition mechanisms are discussed. The interactions that are responsible for single and double capture processes are discussed, and the role of interelectronic repulsion in the double capture process is clarified.

Total and differential charge transfer cross sections in H++Na(3s) or Na*(3p) collisions

Proton-sodium charge transfer is studied, using 9- and 19-state adiabatic molecular bases and the impact parameter method, in the energy range 0.5-5 keV. The dynamical radial and rotational coupling terms and a common translation factor (CTF) are included. The effect of the choice of the coordinate centre on the total charge exchange cross sections to H(n=2) is clearly demonstrated when no CTF is included. The alignment dependence of the capture to H(n=2) is obtained and is satisfactorily compared with the atomic expansion calculations. State-to-state charge exchange differential cross sections are calculated; the alignment and orientation effects are expected to be observable at the collision energy 0.5 keV where they are spread out at scattering angles theta >0.1'.

Collisions of kilo-electron-volt H+ and He+ with molecules at small angles: Absolute differential cross sections for charge transfer.

Absolute differential cross sections for charge-transfer scattering of ${\mathrm{H}}^{+}$ and ${\mathrm{He}}^{+}$ from molecules are reported over the laboratory angular range 0.02\ifmmode^\circ\else\textdegree\fi{}--1.0\ifmmode^\circ\else\textdegree\fi{}. Cross sections have been determined at 0.5, 1.5, and 5.0 keV for collisions of ${\mathrm{H}}^{+}$ with ${\mathrm{N}}_{2}$ and ${\mathrm{O}}_{2}$, and at 1.5 keV for collisions of ${\mathrm{H}}^{+}$ with CO, ${\mathrm{CO}}_{2}$, NO, and ${\mathrm{CH}}_{4}$, and of ${\mathrm{He}}^{+}$ with ${\mathrm{H}}_{2}$, ${\mathrm{N}}_{2}$, ${\mathrm{O}}_{2}$, CO, and NO. The data exhibit considerable structure over the experimental angular range. Absolute integral cross sections from 0\ifmmode^\circ\else\textdegree\fi{} to 1.0\ifmmode^\circ\else\textdegree\fi{} have been obtained and are compared with the published total cross sections.

Theoretical study of differential charge-transfer cross sections for Ne4++He collisions at low energies.

A quantal two-channel calculation is applied to study charge-transfer differential cross sections in ${\mathrm{Ne}}^{4+}$ on He collisions at laboratory impact energies from 220 to 500 eV. The experimental data of Tunnell et al. were used to fit empirical potential curves and coupling terms from which the observed oscillatory structures in the differential cross sections were analyzed. In contrast with the double-charge-transfer process in ${\mathrm{C}}^{4+}$ on He, where the oscillations in the differential cross sections are attributed to pure Stueckelberg oscillations, we demonstrated that the differential cross sections for charge transfer in ${\mathrm{Ne}}^{4+}$ on He exhibit many fine fast oscillations and the observed structures are due to the envelopes of these unresolved fast oscillations. Classical deflection functions are used to help in interpreting the calculated oscillations.

Polarization Dependence of Resonant Charge Transfer in Low-Energy Collisions ofNa+with Laser-ExcitedNa*(3p)

Relative differential cross sections for charge-transfer scattering have been measured over the collision energy range ${E}_{\mathrm{c}.\mathrm{m}.}=45\ensuremath{-}75$ eV. With linearly polarized light exciting $\mathrm{Na}(3s)$ to ${\mathrm{Na}}^{*}(3p)$, the dependence of the charge-transfer cross section on the predominant preparation of the $\ensuremath{\Sigma}$ or $\ensuremath{\Pi}$ excited states of the ionic quasimolecule ${\mathrm{Na}}_{2}^{+}$ has been studied. The results are compared to simple model calculations. It is found that the resonant charge exchange is most probable for the predominant preparation of the ${{\mathrm{Na}}_{2}}^{+}(2{\ensuremath{\Sigma}}_{\mathrm{g},\mathrm{u}})$ excited states.

The effect of reactant vibrational state on differential charge transfer cross sections for T 2+(X 2 Σ g+, ν 0′) + T 2(X 1 Σ g+, ν 0″) collisions

Differential charge transfer cross sections for reactions of vibrationally excited incident ions and molecules have been computed for the T 2 +(X 2 Σ g +, ν 0′) + T 2(X 1 Σ g +, ν 0″) system. Differential cross sections for the formation of neutral products become more intense and concentrated in the forward direction as the quantum number of the reactant ion and/or molecule is increased.

Differential cross sections for charge transfer in collisions of He+, Ne+ and Ar+ with Kr

Differential charge transfer cross sections for collisions of He+, Ne+ and Ar+ with Kr were measured at collision energies below 500 eV. A remarkable fraction of these collisions (2–30 %) occurs with large momentum transfer and small impact parameters. These close collisions lead to an excitation of the product particles, the measured reaction channels are strongly endothermic. In the system Ar++Kr one reaction channel may be described in terms of a curve crossing.

Measurement of Differential Charge-Transfer Cross Sections and Probabilities by Photon-Particle Coincidence Technique

The probabilities and differential cross sections for charge transfer to the $2p$ state of hydrogen in 4- to 20- keV proton-helium collisions have been measured for specific impact parameters by detecting in delayed coincidence the scattered neutral hydrogen atom and the resulting $2p\ensuremath{-}1s$ Lyman-$\ensuremath{\alpha}$ photon. These $2p$ probabilities are compared with the total charge transfer and $2s$ state probabilities, and with the coupled atomic state calculations of Sin Fai Lam.

Collision Spectroscopy. III. Scattering in Low-Energy Charge-Transfer Collisions ofHe+and Ar

Differential charge-transfer cross sections $\ensuremath{\sigma}$ are measured for ${\mathrm{He}}^{+}$ in Ar at energies $E$ from 65 to 300 eV and angles $\ensuremath{\theta}$ from 1\ifmmode^\circ\else\textdegree\fi{} to 30\ifmmode^\circ\else\textdegree\fi{}. The relative measurements are calibrated by comparison with total charge-transfer measurements of Koopman. From reduced plots of $\ensuremath{\rho}=\ensuremath{\theta}sin\ensuremath{\theta}\ensuremath{\sigma}(\ensuremath{\theta})$ versus $\ensuremath{\tau}=E\ensuremath{\theta}$, two, and perhaps three families of oscillations are identified, with reduced angular thresholds at $E\ensuremath{\theta}\ensuremath{\cong}300,970, \mathrm{and} 1250$ eV deg and with spacing $\ensuremath{\Delta}\ensuremath{\theta}$ between peaks near threshold related to the wave number $k$ by the rule $\ensuremath{\Delta}b=(\frac{2\ensuremath{\pi}}{k\ensuremath{\Delta}\ensuremath{\theta}})\ensuremath{\cong}0.51,0.25, \mathrm{and} 0.09$ a. u., respectively. Using potential curves constructed from earlier information on elastic scattering, the first family is identified as arising from a crossing at 2.9 a. u. to a state dissociating to $\mathrm{He} (1{s}^{2})+{\mathrm{Ar}}^{+}(3s3{p}^{6})$, and the second from a crossing at 2.3 a. u. to a state producing $\mathrm{He} (1s2s)+{\mathrm{Ar}}^{+}(3{s}^{2}3{p}^{5})$. Further crossings at distances between 2.25 and 1.95 a. u. leading to other excited-state channels are apparently responsible for more than half of all the charge transfer at these energies.