State-selective K-K electron transfer and K ionization cross sections for Ar and Kr in collisions with highly charged C, O, F, S, and Cl ions at intermediate velocities B. B. Dhal, 1, * Lokesh C. Tribedi, 1,† U. Tiwari, 1 K. V. Thulasiram, 1 P. N. Tandon, 1 T. G. Lee, 2 C. D. Lin, 2 and L. Gulya ´ s 3 1 Tata Institute of Fundamental Research, Homi Bhabha Road, Colaba, Mumbai 400 005, India 2 JR Macdonald Laboratory, Department of Physics, Kansas State University, Manhattan, Kansas 66506 3 Institute of Nuclear Research of the Hungarian Academy of Science (ATOMKI), P.O. Box 51, H-4001 Debreccen, Hungary Received 7 March 2000; published 19 July 2000 We have measured the single K -K electron-transfer cross sections along with the single K-shell ionization cross sections of Ar induced by H-like and bare C,O, and F projectiles, and of Kr by F, S, and Cl ions in the energy range 1.5–6 MeV u -1 . The target x-ray yields as a function of the number of K shell vacancies in the incident beam were used to derive the K ionization cross sections of the targets and the K -K i.e., target K shell to projectile K shell electron-transfer cross sections. The enhancement in the fluorescence yield due to mul- tiple vacancies in the target atom was deduced from the energy shifts and intensity ratios of the characteristic x-ray lines to derive vacancy production cross sections from the measured x-ray production cross sections. The energy shifts of K x-ray lines were found to be dependent on the incident charge states of the projectiles. Continuum-distorted-wave eikonal-initial-state calculations are found to underestimate the ionization cross- section data in general, and the deviations are most pronounced for Kr. Perturbed stationary-state calculations, including corrective terms due to energy loss, Coulomb deflection, and relativistic wave function, agree with the data only for asymmetric collisions ( Z 1 / Z 2 0.4), and largely overestimate for relatively symmetric sys- tems. The K -K electron-transfer cross sections are well reproduced by the two-center close-coupling calcula- tions for both targets except, for the asymmetric collisions. The perturbed stationary state PSS calculations of Lapicki and McDaniel are also used to explain the K -K electron-transfer data for the asymmetric systems. In addition, the K -L electron-transfer cross sections are also measured for S and Cl ions on Kr, and compared with the PSS calculations. PACS numbers: 34.50.Fa, 34.70.+e I. INTRODUCTION Ionization, electron capture, and excitation are among the most important inelastic processes in ion-atom collisions. At intermediate velocities, i.e., when the projectile velocity ( v p ) is approximately equal to the orbital velocity ( v e ) of the active electron, the strengths of these processes are of the same orders of magnitude, and a coupling among these dif- ferent channels become important. Ionization and electron transfer involving deeply bound inner shells play major roles in producing vacancies in these shells in heavy ion-atom collisions. In some cases, depending on the symmetry pa- rameter of the collision system the electron-transfer channel could be much larger than the direct Coulomb ionization. There have been numerous studies on the total electron cap- ture of the initially loosely bound electrons, and several em- pirical scaling laws 1,2 have been proposed to predict the capture cross sections which are found to fall rapidly ( v p -11 ) with the projectile velocity. On the other hand, for the projectiles with energies of the order of magnitude of hundreds of MeVs, the cross sections for a deeply bound electron transfer such as  K-K ) process are expected to reach a maximum, since the projectile velocity ( v p ) is ap- proximately the same as the orbital velocity ( v e ) of the ac- tive electron, as in the present studies. State-selective electron-transfer cross sections involving deeply bound ini- tial and final states cannot be described by such empirical laws, and the mechanism of such transfer processes in strongly perturbative collisions is not yet completely under- stood. The initial- and final-state binding energies of the transferred electron, the symmetry parameter S z =Z 1 / Z 2 , and the reduced velocity v r =v p / v e of the collision system are the relevant parameters which are generally used to de- scribe the transfer process. Here Z 1 and Z 2 refer to the atomic numbers of the projectile and the target, respectively. The binding energy matching between the initial and final states provides a favorable condition for the electron-transfer process, as predicted by first-order calculations. Single K -K electron-transfer cross sections have been measured in a few cases in the past, and mostly using solid targets 3–6, in which the evolution of the vacancy configu- rations due to multiple collisions inside the target compli- cated the data analysis. A three-component model is gener- ally used see references in Ref. 7 to fit the observed thickness dependence of the x-ray yields for different initial- charge states of the projectiles. These curves are then pro- jected at zero thickness in order to extract the ionization and the electron-transfer cross sections. Some measurements are even carried out with a single thin target, and, as the mea- sured values of the electron-transfer cross sections are quite large, the reported values might be dependent on the thick- ness of the target used due to the initial very steep thickness dependence of the charge states of the ion inside the solid. This is certainly true for incident charge states of the incident *Present address: School of Physics, University of Melbourne, Parkville, Vic-3052, Australia. † Corresponding author: Email address: lokesh@tifr.res.in PHYSICAL REVIEW A, VOLUME 62, 022714 1050-2947/2000/622/0227149/$15.00 ©2000 The American Physical Society 62 022714-1