H. Martínez

The influence of ion/molecule reactions on the evaluation of ion mobility and diffusion coefficients

Abstract This paper deals with the evaluation of the mean and the variance of the ion flux at the exit of a drift tube, from which the drift velocity, νd, and the longitudinal diffusion coefficient, DL, can be derived. Besides drift and diffusion, the presence of a primary ion conversion process through reactions with the gas is fully considered from the outset. Full expressions for the mean and variance of the ion flux are then approximated by resorting to experimental conditions in which low ionic reactivity, adequate drift tube geometry, and other experimental conditions are met, thus arriving at very simple expressions from which νd and DL are derived. These simple expressions have been obtained previously from analyses ignoring ion/molecule reactions from the outset. The full expressions derived here and their approximations are used to provide a means of evaluating the errors incurred when very simple expressions are used in highly reacting ion/neutral systems.

Single electron capture in low-energy Kr+He collisions

Abstract Absolute differential and total cross sections for electron capture have been measured for Kr+ incident on He at impact energies between 1.0 to 5.0 keV and over the laboratory angular range −3° to 3°. The reduced differential cross sections present a maximum at a value of τ 2~ 1.3 keV deg independent of energy. The behaviour of the measured cross sections is compared with a semi-empirical model for near-resonant charge transfer.

A Survey of Recent Research on Ion Transport in Sf6

A compilation of recent experimental work on the mobility and longitudinal diffusion of SF6ions in their parent gas is presented and critically evaluated. Some progress in the extension of the E/N and pressure ranges over earlier work is observed. With the exception of very recent, mass-identified data for two positive ions, all other data have been derived from experiments lacking mass-analysis. The need for mass-analyzed data is stressed

Single-electron capture cross section in 1-500 keV H+-Mg collisions

Total and partial cross sections for single-electron capture of H+ on Mg atoms have been calculated by the semi-classical impact-parameter method, using a two-centre atomic basis expansion, for energies between 1 and 500 keV. The present cross sections are in good agreement with previous experimental data over the wide energy range considered in this paper. The calculated capture cross section into the 2s state of hydrogen reproduces the main qualitative features observed experimentally but quantitatively overestimates the experimental measurements by a factor of four. However, our calculations show, for the first time, that capture into the n = 2 levels of hydrogen could be as important as capture into the ground state.

SINGLE ELECTRON CAPTURE OF H+ IN MG IN THE ENERGY RANGE 0.5 TO 5.0 KEV

Absolute differential and total cross sections have been measured for the single electron capture of Ne+ in He at impact energies between 0.5 and 5 keV. Oscillations in the differential cross sections are interpreted as the envelope of the fast oscillations due to the interference of the scattering amplitudes. Total cross sections are in agreement with previous experiments.

Translational spectroscopy of H− produced by collision induced dissociation of H3+ on He

Abstract From the laboratory energy distributions of H − , resulting from collision induced dissociation of the H 3 + molecular ion in He at incident energies of 2.75 keV and 3.8 keV, it was possible to construct the potential energy curve in the Franck-Condon region for the excited state of H 3 + which converges asymptotically to H + + H − + H + , using an inversion method.

Single electron capture in He+ on SF6, collisions at low keV energies

Abstract We have measured the absolute differential and total cross sections for single electron capture from He + ions on SF 6 in the energy range 1.0 to 5.0 keV. The total collisional destruction cross sections of He Rydberg atoms on SF 6 has been compared with the sum of the available free electron cross sections (for equal velocity) and the present absolute total cross sections. The results support the validity of the independent particle model for the destruction of Rydberg atoms over this range of energies.

Angular distributions of H− fragments from H+2 on Mg at low keV collisions

Abstract Three interesting structures have been observed on the angular distributions of the H− fragments produced by the collision of H+2 on Mg at projectile energies of 1, 2, 3, 4 and 5 keV. The good matching of the distributions to the a scaling law ( 1 E inc ) dσ dω = ƒ(E inc θ 2 ) indicates that the same mechanism is acting over this range of energies. The mechanism proposed for the production of H− is through the predissociative states of H+2 interacting with the target.

Collisional dissociation and binding energy of D3

Abstract For collision energies between 2 and 5 keV the collision induced dissociation of D 3 + colliding with He was measured. Both angular and energy distribution of D 2 + fragment were obtained. Due to the correlation between center of mass energy distributions of the dissociating fragments and their angular spread in the laboratory frame, the results from both measurements are used to estimate the binding energy of the triatomic molecular ion D 3 + . The measured value of 6.54 ± 0.52 eV below the dissociation energy agrees well with previous theoretical predictions and experiment of its stable isotopic variant H 3 + .

The collisional dissociation of HD+2 studied by angular distributions and translational spectroscopy

Abstract Collisional dissociation of HD+2 molecular ion incident on He has been studied in the energy range 1 to 5 keV by angular distributions and translational spectroscopy. From the angular and velocity spectra of HD+ and D+2, we have calculated the binding energy of HD+2, some of the main transitions involved in the dissociation process, and the total cross sections for the production of both fragments.