R.H. McFarland

Resonant-transfer-and-excitation for highly charged ions (16 ≤ z ≤ 23) in collisions with helium

Abstract Significant new evidence is presented for resonant-transfer-and-excitation (RTE) in ion-atom collisions. This process occurs when a target electron is captured simultaneously with the excitation of the projectile followed by deexcitation via photon emission. RTE, which is analogous to dielectronic recombination (DR), proceeds via the inverse of an Auger transition, and is expected to be resonant for projectile velocities corresponding to the energy of the ejected electron in the Auger process. RTE was investigated by measuring cross sections for projectile K X-ray emission coincident with single electron capture for 15–200 MeV 16 S 13+ , 100–360 MeV 20 Ca 16+,17+,18+ and 180–460 MeV 23 V 19+,20+,21+ ions colliding with helium. Strong resonant behavior, in agreement with theoretical calculations of RTE, was observed in the coincidence cross sections.

K- and l-shell resonant transfer and excitation in ion-atom collisions

Recent experimental studies of resonant transfer and excitation (RTE) in ion-atom collisions are reviewed. In the RTE process correlated electron capture and projectile excitation occur together in a single encounter with a target atom. Measurements of Ca/sup q+/ + H/sub 2/ (q = 10 to 19) from 100 to 370 MeV establish the projectile charge-state dependence of K-shell RTE and provide a detailed test of the theory. Structure due to RTE is observed in the energy dependence of the total electron-capture cross sections for this collision system. A comparison of the Ca/sup 17 +/ + H/sub 2/ data with previous results for Ca/sup 17 +/ + He demonstrates the effect of the target-electron momentum distribution on the RTE process. Studies of 230 to 610 MeV Nb/sup 31 +/ + H/sub 2/ provide information about RTE involving agreement with theoretical calculations. 15 refs., 4 figs.

L-SHELL RESONANT TRANSFER AND EXCITATION FOR NE-LIKE NIOBIUM IONS

Projectile excitation and charge transfer (capture) can occur simultaneously in a single encounter with a target atom through the electron-electron interaction between a projectile electron and a weakly bound target electron. This process is referred to as resonant transfer and excitation (RTE). L-shell RTE has been investigated for 230 to 610 MeV Nb/sup 31 +/ (neonlike) ions incident on H/sub 2/. 11 refs., 1 fig. (WRF)

ELECTRON LOSS AND EXCITATION IN COLLISIONS OF HIGHLY CHARGED CALCIUM-IONS WITH H2 AND HE

Cross sections for projectile electron loss and excitation (LE) in single collisions of 150–360 MeV calcium ions with H2 and He have been measured for projectile charge states in the range 12 + to 19 +. The results establish that for the present collision partners projectile K X-ray production takes place through the excitation rather than removal of a ls electron.

Ion-X-ray coincidence measurements in heavy ion collisions

Abstract X-ray emission associated with projectile charge-changing events in fast ion-atom collisions can be used to isolate and investigate excitation, ionization and charge transfer, as well as combinations of these processes. The major emphasis to date has been on the study of two-electron processes. Several such processes have been studied in detail. Resonant and nonresonant transfer and excitation (RTE and NTE) occur when electron capture and projectile excitation, with stabilization by X-ray emission, take place together in a single collision. Loss and excitation (LE) occurs when a projectile electron is removed and the ion is excited in a single collision. The cross sections for loss and excitation have been measured for a wide range of highly stripped projectiles over a broad energy range. The results shed light on projectile K X-ray production processes in heavy-ion collisions. The use of ion-X-ray coincidence techniques in exploring these and other collision processes will be discussed.

Charge transfer and excitation in high-energy ion-atom collisions☆

Abstract Coincidence measurements of charge transfer and simultaneous projectile electron excitation provide insight into correlated two-electron processes in energetic ion-atom collisions. Projectile excitation and electron capture can occur simultaneously in a collision of a highly charged ion with a target atom; this process is called resonant transfer and excitation (RTE). The intermediate excited state which is thus formed can subsequently decay by photon emission or by Auger-electron emission. Results are shown for RTE in both the K-shell of Ca ions and the L-shell of Nb ions, for simultaneous projectile electron loss and excitation, and for the effect of RTE on electron capture.

RESONANT-TRANSFER-AND-EXCITATION FOR HIGHLY CHARGED IONS (16 LESS-THAN-OR-EQUAL-TO Z LESS-THAN-OR-EQUAL-TO 23) IN COLLISIONS WITH HELIUM

Significant new evidence is presented for resonant-transfer-and-excitation (RTE) in ion-atom collisions. This process occurs when a target electron is captured simultaneously with the excitation of the projectile followed by deexcitation via photon emission. RTE, which is analogous to dielectronic recombination (DR), proceeds via the inverse of an Auger transition, and is expected to be resonant for projectile velocities corresponding to the energy of the ejected electron in the Auger process. RTE was investigated by measuring cross sections for projectile K x-ray emission coincident with single electron capture for 15 to 200 MeV /sub 16/S/sup 13 +/, 100 to 360 MeV /sub 20/Ca/sup 16 +/ /sup 17 +/ /sup 18 +/ and 180 to 460 MeV /sub 23/V/sup 19 +/ /sup 20 +/ /sup 21 +/ ions colliding with helium. Strong resonant behavior, in agreement with theoretical calculations of RTE, was observed in the coincidence cross sections.