Charge-transfer cross sections in collisions of ground-state Ca and H+

We have investigated collisions of Ca(4s(2)) with H+ in the energy range of 200 eV/u-10 keV/u using the semiclassical molecular-orbital close-coupling (MOCC) method with 18 coupled molecular states (11 (1)Sigma(+) and seven (1)Pi(+) states) to determine charge-transfer cross sections. Except for the incoming channel 6 (1)Sigma(+), the molecular states all correspond to charge-transfer channels. Inclusion of Ca2+-H- is crucial in the configuration-interaction calculation for generating the molecular wave functions and potentials. Because of the Coulomb attraction, the state separating to Ca2+-H- creates many avoided crossings, even though at infinite separation it lies energetically above all other states that we included. Because of the avoided crossings between the incoming channel 6 (1)Sigma(+) and the energetically close charge-transfer channel 7 (1)Sigma(+) the charge-transfer interaction occurs at long range. This makes calculations of charge-transfer cross sections by the MOCC method very challenging. The total charge-transfer cross sections increase monotonically from 3.4x10(-15) cm(2) at 200 eV/u to 4.5x10(-15) cm(2) at 10 keV/u. Charge transfer occurs mostly to the excited Ca+(5p) state in the entire energy range, which is the sum of the charge transfer to 7 (1)Sigma(+) and 4 (1)Pi(+). It accounts for similar to 47% of the total charge transfer cross sections at 200 eV/u. However, as the energy increases, transfer to Ca+(4d) increases, and at 10 keV/u the charge-transfer cross sections for Ca+(5p) and Ca+(4d) become comparable, each giving similar to 38% of the total cross section.