Nuclear Instruments and Methods in Physics Research B79 (1993) 8-10 North-Holland NUMI zyxwvutsrqpo B zyxwvutsrqp Beam Intemctionr with Materials P Atoms Possible two-electron excitations in C3+ following 1 MeV/u collisions with atomic targets; 2 = 2, 10, 18 and 36 E.F. Deveney, Q.C. Kessel, R.J. Fuller and M.P. Reaves zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQ Depatiment of Physics and the Institute of Materials Science, The University of Connecticut, Storm, CT 06269, USA S.M. Shafroth Department of Physics and Astronomy, Size University of North Carolina at Chapel Hill, Chapel Hill, NC 27599-3255, USA N. Jones Physics Division, Oak Ridge National Laboratory, Oak Ridge, TN 37831, USA Auger electrons emitted from Li-lie carbon projectiles excited during 1 MeV/u collisions with atomic targets (Z = 2, 10, 18 and 36) have been measured. As a function of the target Z, we observe the yields of singly and doubly excited autoionizing (AI) configurations of C’+ excited during the collision that decay to the {l~*(~S)+e,l,}~L ground state. The investigation focuses on Auger electrons emitted with energies between 220 and 260 eV in the projectile reference frame. In addition to the singly excited (1~2s21)~L AI configurations expected from projectile 1s electron excitation, doubly excited states to the {1~(2p*)‘D)~D and {ls(2p2)‘S)% are also observed with increasing intensities in going from He to the higher Z targets. If the 2D and the 2S peaks are the result of two-electron excitations, it may be possible to investigate this aspect of the collision using some of the recent approaches taken in studying the excitations of the two electrons in He targets. 1. Introduction The projectile Auger electron spectra following col- lisions of Li-like carbon projectile ions with single He atom targets provides unique information on the ion- atom many-body collision interaction. The identifica- tion of Auger peaks in the emitted electron spectra with intermediate autoionizing (AI) configurations of the projectile states formed by the collision can help to decipher the role which specific individual interactions play. Previous studies have investigated the following projectile-target interactions in ion-atom collisions. The projectile electron with the target electron (elec- tron-electron or e-e) interaction, the projectile elec- tron with the target nucleus (electron-nucleus or e-n) interaction, the projectile nucleus with the target elec- tron (nucleus-electron or n-e) interaction and various combinations thereof. For fast collisions in the impulse approximation, target electrons can be viewed as “quasi-free” and one possible n-e interaction is the capture of a target electron onto the projectile, ion. Combining this capture in various combinations with the aforementioned interactions can result in resonant, nonresonant and unwrrelated capture channels and processes such as: resonant transfer and excitation (RTE), nonresonant transfer excitation (NTE) and un- correlated transfer and excitation CUTE) such as 2eTE which is uncorrelated two electron transfer and excita- tion [l-4]. In this work we investigate the Auger electron spec- tra of C3+ following collisions with different-Z atomic targets at 1 MeV/u. The investigation focuses on the relative intensities of Auger peaks between 220 to 260 eV (projectile frame) in going from collisions with He, Ne, Ar to Kr targets. In particular, the roles of some of the previously mentioned interactions as a function of the target 2 and target electrons are discussed with respect to the present data. 2. Experiment and results The experiment was performed at Oak Ridge Na- tional Laboratory (ORNL) using 12 MeV C3+ beams from the EN Tandem accelerator. Typically, 300 nA particle currents were passed through the He, Ne, Ar and Kr gas targets under single-collision conditions. Electrons emitted at lo” in the laboratory frame en- tered a parallel plate double-pass electron spectrome- ter that was designed and constructed by Giese and Bechthold [5] at ORNL and was based on the original Swenson spectrometer design [6]. Energies tabulated 0168-583X/93/$06.00 8 1993 - Elsevier Science Publishers B.V. All rights reserved