A classical analysis of proton collisions with ground-state and excited, aligned sodium targets

Abstract

The dependence of electron capture and ionization processes on the pre-collision electronic distribution is examined for the systems primarily in the energy range 1 - 15 keV. Populations of the capture and ionization channels as well as the coherence of the post-collision electronic distribution of the capture product are formulated using the classical trajectory Monte Carlo (CTMC) method. Total capture and ionization cross sections arising from initially aligned Na(3p) targets exhibit transient behaviour near the velocity-matching energy of 5.7 keV. This observation is described in terms of anisotropy parameters; anisotropy effects are also analysed for the capture states n = 2, 3 and 4. In addition to the population manifold, we present theoretical calculations of the alignment parameter and the z-component of the dipole moment , in order to relate the alignment of the post-collision charge cloud to that of the initial Na(3s, , ) target states. The z-component of the cross product of the angular momentum and the Runge - Lenz vector is used to describe the orientation of the post-collision product generated from the aligned Na(, ) pre-collision reactants.

Single ionization of Na(3s) and Na*(3p) by low energy ion impact

“…Later a generalized scaling law Figure 3. Absolute single ionization cross sections for different projectiles colliding on both Na(3s) and Na * (3p), including TC-BGM calculations for H + +Na(3s) [13] (--) and CTMC calculations for H + +Na * (3p) [22] (----) and He 2+ +Na(3s) [14] [10,11], also showing their result of a fit of H and He data.…”

“…The absolute cross sections for single ionization of Na * (3p) were obtained using the cross sections for capture from Na(3s) and applying the cross section ratio between Na(3s) and Na * (3p). Theoretical cross sections are available from TC-BGM (H + +Na(3s) [13]) and classical trajectory Monte Carlo (CTMC) calculations (H + +Na * (3p) [22], He 2+ +Na(3s) [14]). Note that for the H + +Na(3s) system CTMC calculations [22] yield about 20-25% smaller cross sections compared to the TC-BGM calculations.…”

“…Theoretical cross sections are available from TC-BGM (H + +Na(3s) [13]) and classical trajectory Monte Carlo (CTMC) calculations (H + +Na * (3p) [22], He 2+ +Na(3s) [14]). Note that for the H + +Na(3s) system CTMC calculations [22] yield about 20-25% smaller cross sections compared to the TC-BGM calculations.…”

Orientation effects for collisions at energies beyond the `velocity-matching' region

“…At these projectile energies it is now well established that an expansion of the wavefunction in either atomic (AO) or molecular (MO) basis states is adequate and, in general, gives an excellent agreement with experiments for total and partial cross sections [4] and phase-dependent coherence parameters [3,5]. Recently, it has also been demonstrated that the classical trajectory Monte Carlo (CTMC) method gives the correct relative distribution for the H(n = 2) channels in capture from laser-excited Na(3p −1 ) [6][7][8][9]. At higher energies much less is known about the state-to-state dynamics in collisions between charged particles and laser-excited atoms.…”

Left/right capture asymmetry in He2+-Na(3p-1) collisions: classical versus quantal collision dynamics

“…Thus total and state-to-state asymmetries in differential scattering may now be studied and compared to theory at the most fundamental level of one-electron quantum dynamics. Since the classical trajectory Monte Carlo (CTMC) method has been used with various degrees of success for many such related studies also involving ionization [3][4][5][6][7], one may ask whether there are any distinct quantum signatures at all involved in the collision dynamics. Our previous studies of collisions between singly charged ions and excited atoms have displayed, however, some clear discrepancies for electron capture.…”