Density matrices of the n=2 and 3 manifolds of H atoms produced in p-H collisions at 1-50 keV impact energies

Abstract

Abstract. We study the full density matrices (differential as well as integrated with respect to impact parameter) for charge transfer and excitation to the n = 2 and 3 manifolds of the excited hydrogen atoms formed in p-H collisions over impact energies 1-50 keV. The scattering amplitudes are determined using the modified two-centre atomic-orbitalexpansion method (ao+) based on the impact parameter formalism. From these scattering amplitudes several physical parameters such as the dipole moment, velocity vector, charge density and current distribution are extracted. The analysis of these parameters allows us to provide an approximate classical orbital picture for excitation and charge transfer to each manifold at both the low ( E < 5 keV) and intermediate ( E > 20 keV) energy regions.In general, we can interpret the charge distribution around each centre after the collision as resulting from the electron cloud being pulled apart between the two collision centres as they move away from each other. Comparison is also made with the electron charge density for the n = 2 manifold of H in electron-hydrogen and positron-hydrogen impact excitations at 50-200 eV using the calculation of van Wyngaarden and Walters.

Coherence parameters of atomic excited states: comparison of results from the CTMC and the quantal calculations

“…These coherence parameters, for example the orientation and alignment parameters, the dipole moment of the degenerate excited states of atomic hydrogen, can be determined experimentally by measuring the angular distribution and/or polarization of the emitted radiations [1,3] with or without an external electric field. These parameters have been calculated theoretically by the distorted wave Born approximation for collisions of electrons and positrons with atoms [-4-6], and by the close-coupling method for collisions of heavy ions with atoms [7][8][9][10][11][12]. In general, these quantal and semiclassical calculations are in reasonable agreement with experimental data [1,2].…”

“…However, recall that the trajectories described by the semiclassical theory and the CTMC are different for large impact parameters. The calculation of dipole moments and orientation parameters from the scattering amplitudes in the semiclassical close-coupling (CC) theory has been discussed previously [7][8][9]. For p -H collisions at 50 keV, the dipole moments from the close-coupling calculation have been discussed in Jain et al [-8].…”

“…The present calculation used a much larger basis set (44 states) than the previous one in [8] (28 states). At 50 keV for p-H collisions, ionization cross section is quite large.…”

Analysis of impact-excited HeI states by applying magnetic and electric depolarization techniques

“…When referring to a perturbed stationary state approximation [31], this momentum conservation implies that the electron cloud should be endowed with inertia which keeps it moving on with its original velocity when its binding particle-system changes. Pictorially the effect of this inertia can be seen in contour plots of electronic charge distributions as a function of time for protonhydrogen collisions [32,33]. Though the authors who calculated these density distributions related the elongation of the final distributions into the direction of the collision partner to its "dragging" [32] or "attractive" [33] residual Coulomb force, we believe that the asymmetry is more correctly ascribed to the inertia of the electron cloud.…”

“…Pictorially the effect of this inertia can be seen in contour plots of electronic charge distributions as a function of time for protonhydrogen collisions [32,33]. Though the authors who calculated these density distributions related the elongation of the final distributions into the direction of the collision partner to its "dragging" [32] or "attractive" [33] residual Coulomb force, we believe that the asymmetry is more correctly ascribed to the inertia of the electron cloud. Indeed, our experiments on He-He collisions were started to investigate impact excitation where a residual Coulomb force acting on the excited electron can be excluded.…”