Orientation parameters and dipole moments of He⁺(n=2) states in He²⁺+H collisions: comparison of CTMC and close-coupling results

Abstract

The orientation parameter and the dipole moment of the n=2 states of He+ resulting from electron capture in He2++H collisions are examined using the classical trajectory Monte Carlo (CTMC) method and the close-coupling expansion using two-centre atomic orbitals at 10, 25 and 50 keV amu-1. It is shown that the orientation parameters calculated from the two theories are in good agreement but large discrepancies exist for the dipole moments. Together with previous similar comparisons for p-H collisions, the authors conclude that the CTMC method is not reliable in predicting the coherence parameters of excited states formed in atomic collisions.

Coherence parameters for He+(2p) capture and H(2p) excitation in He2+-H(1s) collisions

“…To emphasize the most important b and 0 ranges we have chosen here to display the reduced probability (b times probability) and the reduced differential cross section (sin(0) times da/df2). We find fair to good agreement with the trajectory results of Toshima et al [15], best at 25 keV (and at 50 keV/amu not displayed). The differential cross sections for capture into oriented states, obtained by the eikonal method from Bessel-transforms of the classical trajectory amplitudes [9,29], display a smooth dependence upon scattering angle.…”

“…In order to compare with recent results of Toshima et al [15], and to extend our predictions to the experimental differential level, we present in Fig. 9 the He ÷ (2s/2p) capture probabilities and the He ÷ (2p) orientation parameter as functions of b at the important impact [15], and into He+(2p), solid line present calculation and long~short dashed line Toshima et al [15], and in the panels below the corresponding 2p orientation parameter L±, as functions of impact parameter b and scattering angle 0, respectively, a at impact energy 10 keV/amu, and b at 25 keV/amu.…”

“…9 the He ÷ (2s/2p) capture probabilities and the He ÷ (2p) orientation parameter as functions of b at the important impact [15], and into He+(2p), solid line present calculation and long~short dashed line Toshima et al [15], and in the panels below the corresponding 2p orientation parameter L±, as functions of impact parameter b and scattering angle 0, respectively, a at impact energy 10 keV/amu, and b at 25 keV/amu. Note that the classical trajectory probabilities and the differential cross sections shown refer to left side passages and left side scattering, respectively, Le.…”

“…To the best of our knowledge no experimental data for differential cross sections, alignment or orientation parameters have been published. Winter and Lane [14] give the theoretical total capture probability as a function of impact parameter and recently the He2+(2p) orientation parameter has been calculated at 10, 25 and 50 keV/amu by Toshima et al [15], allowing a comparison at this detailed level as well.…”