Projectilendistributions following charge transfer ofAr+andNa+

Abstract

The n distributions produced by charge transfer of Ar+ and Na+ ions in a target of Na(nl) Rydberg atoms were extensively measured at intermediate velocities. The 60 -2100-eV ions bombarded a laser-excited atomic-beam target. The projectiles were neutralized by capture into Rydberg states of Ar and Na and were analyzed by field ionization in an inhomogeneous-field detector whose response over states and energies was carefully mapped. The choice of initially prepared Na states, 24d, 25s, 28d, 29s, 33d, and 34s, allowed a comparison of 1=0 and~2 targets at nearly equal binding energies over a range of reduced velocity u=0. 187 to 1.95. Capture populates m sublevels broadly, not merely m =0. Overlapping contributions from adiabatic and diabatic modes of field ionization were accommodated in the analysis, which used a maximum-entropy-principle parametric form to fit the observed final-state distributions. The peak of the distributions, n, ", shifts upward from a value less than the initial state n, to a value one to three units higher than n, at U between 0.7 and 0.9 and ultimately shifts downward below n; as 0 is further increased. The distributions become significantly sharper where the maximum upward shift occurs. Two ratios were defined to express the widths of fina-state distributions in relative terms, one measuring the spread of orbital kinetic energy and the other the spread of Bohr-orbit velocity. By these ratios a universal behavior over energies, states, and projectile species is observed, and small differences between l =0 and~2 targets may be seen. A theoretical understanding of the present results, which span velocities where both molecular and perturbative theories are normally used, will require a quantal formulation that models the free-ranging response that is a hallmark of the high-quantum-number lim-it.

A classical analogue for adiabatic Stark splitting in non-hydrogenic atoms

“…As with studies of the simple Stark effect, ion-atom scattering for highly excited states has a long history. For example, [22][23][24] experimentally studied -changing and n-changing collisions as well as charge transfer. Several theoretical studies [25][26][27][28][29] have investigated most aspects of this system.…”

A CTMC Study of Collisions between Protons and H2+Molecular Ions

“…with a preferred sense of circulation of the electron around the nucleus) and also between ions and aligned atoms (where the probability distribution of the electron is not spherical). The interest has been triggered by the development of experimental techniques which allow to prepare atoms in well defined states of low [1] or high quantum numbers (n, l, m) [2] and, after scattering, to measure the final state of the system [3]. The very narrow phase space volume sampled by the electron allows a detailed study of the physical mechanisms occurring during the impact, which would not be otherwise transparent due to the averaging over the entire space of electronic configurations.…”

Energy Transfer in Charge Exchange Collisions between Slow Ions and Rydberg Atoms

“…Electron capture by slow ions from a Rydberg atom is a quasiresonant process in which the most probable binding energy of the captured electron is comparable to its original binding energy in the Rydberg atom target [1]. These collisions can be described in a simple manner classically as a three-body problem, but the quantum mechanical calculation quickly becomes intractable because of the large number of accessible states.…”

“…While some classical models have been used to describe these collisions, notably the classical trajectory Monte Carlo model (CTMC) [2], the limitations of a classical description are not yet clear. Only a limited number of experimental studies have been reported, and these have studied the final state energy distributions indirectly by means of Stark ionization [1,3,4].…”