Absolute cross sections for charge capture from Rydberg targets by slow highly charged ions

Abstract

A crossed beam experiment has been used to measure absolute charge capture cross sections in collisions of slow highly charged xenon ions with laser excited Rydberg atoms. The cross sections were measured for scaled projectile velocities nv" from 1.0 to 6.0, for projectile charges of 8, 16, 32, and 40, where n is the principal quantum number of the target electron. Experimental cross sections are compared with predictions of classical models.PACS number(s): 34.60.+z, 34.70.+e A substantial amount of work has been done investigating charge capture cross sections, both difFerential [1,2] and total [3] in final principal quantum number, for singly charged projectiles incident on target Rydberg atoms. This work has recently been supplemented by studies using Rydberg targets that have been put into circular [4] and elliptical [5] states. None of the above cross sections are absolute. On the theoretical side, while some progress is being made in quantum mechanical calculations [6] through the use of propensity rules, to date, only classical treatments, such as classical trajectory Monte Carlo (CTMC) calculations [7] or the Bohr-Lindhard model [8], are capable of producing predictions of cross sections for these collisions. In order to test the validity of classical calculations, as well as to provide test cases for future quantum mechanical calculations, it is of great current interest to have absolute cross sections for charge capture with Rydberg targets, which are differential in as many parameters as possible, including the projectile charge state. In this work we report absolute charge capture cross sections measured. for the collision system of Xe~+ + Rb(10 f), for q = 8, 16, 32, 40, and for scaled pro-jectile velocities vz/v, between 1.0 and 6.0, where v, is

Absolute charge capture cross sections from a Rydberg target: experimental results and comparison with theoretical models

“…Therefore, the capture when laser 3 is off must be from the ground state, 5s, or intermediate states 5p or 4d. Also, capture from the intermediate states was found to be less than 0.2% [3]. This allows the derivation of the capture probability to be simplified into a two-state (ground state and Rydberg state) system: I on,off 0 : the incoming projectile flux with lasers on or off, respectively; I (x): the projectile flux at position x inside the target; σ g,r : single-capture cross section from ground-or Rydberg-state rubidium, respectively; ρ g,r : density distribution for ground-or Rydberg-state rubidium, respectively; S on,off : the total number of single-capture events with laser on or off, respectively; l g,r : target length for ground-or Rydberg-state rubidium, respectively.…”

“…(Ambient light levels cause a positive bias on the detector output so that the peak on the lower end of the spectrum is offset from 0.) Previous studies [3,11] showed that above a rather low threshold, the number of Rydberg atoms should be a linear function of the intensity of the blue fluorescence. In order to obtain consistently normalized cross sections, the data were re-sorted using blue intensity plots like that in figure 5.…”

“…To date, only classical calculations like CTMC or those based on an over-barrier or Bohr-Lindhard model can be used to predict capture cross sections in high-n collision systems . With one exception [3], all experimental charge capture cross sections from Rydberg states [4][5][6][7], or more recently from elliptical [8] or circular [9] Rydberg states, are relative. It is important to measure absolute cross sections for a wide range of projectile charge states in order to provide a test on the validity of these classical treatments, and also to provide some experimental data for future quantum mechanical calculations, as they become feasible.…”

“…It is important to measure absolute cross sections for a wide range of projectile charge states in order to provide a test on the validity of these classical treatments, and also to provide some experimental data for future quantum mechanical calculations, as they become feasible. In an earlier publication [3], absolute charge capture cross sections were presented for a range of projectile charge states and velocities. In this work, the absolute capture cross sections for (Xe, Ar) q+ on Rb(10f) for an extended range of projectile charge, q = 2, 4, 8, 16, 32, and 40, and for projectile velocities between 0.05 and 0.6 atomic units are reported.…”

Experiments with Highly-Ionized Atoms in Unitary Penning Traps

“…This will be placed orthogonal to the ion path to allow the injection of the rubidium beam into the center of the re-capture Penning trap. A two- [70] or three-laser excitation scheme [71] can be used to excite the rubidium atoms to a Rydberg state. These Rydberg rubidium atoms will be injected into the Penning trap, where they will undergo resonant charge exchange [72] with trapped, fully-ionized helium and neon ions to form one-electron ions in Rydberg states.…”