Electron capture and ionisation in intermediate-energy C$$^{6+}-$$He collisions: Integrated cross sections

Abstract Integrated cross sections for total and state-selective electron capture, and ionisation in C $$^{6+}-$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:mmultiscripts> <mml:mrow/> <mml:mrow/> <mml:mrow> <mml:mn>6</mml:mn> <mml:mo>+</mml:mo> </mml:mrow> </mml:mmultiscripts> <mml:mo>-</mml:mo> </mml:mrow> </mml:math> He collisions are calculated using the two-centre four-body wave-packet convergent close-coupling method for projectile energies ranging from 2 keV/u to 3 MeV/u. The two-electron target structure accounts for electron-electron correlation effects, as well as electron exchange in the rearrangement C $$^{5+}-$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:mmultiscripts> <mml:mrow/> <mml:mrow/> <mml:mrow> <mml:mn>5</mml:mn> <mml:mo>+</mml:mo> </mml:mrow> </mml:mmultiscripts> <mml:mo>-</mml:mo> </mml:mrow> </mml:math> He $$^{+}$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mmultiscripts> <mml:mrow/> <mml:mrow/> <mml:mo>+</mml:mo> </mml:mmultiscripts> </mml:math> channels, which become important at low and intermediate energies. Also used for comparison is an alternative approach that reduces the He target to an effective one-electron system. For electron capture, both methods display good agreement with experiments at high impact energies. For low impact energies the two-electron method performs well, however, the effective single-electron model overestimates available experimental data. Generally good agreement with experiment is found for ionisation cross sections for projectile energies greater than 100 keV/u with both methods. The effective single-electron method is extended down to 10 keV/u, however it overestimates low-energy experiments. It is concluded that the two-electron target description is necessary to correctly model electron capture in the entire range of incident collision energies considered in this work.