MOLECULAR-STATE TREATMENT OF ELECTRON-CAPTURE IN COLLISIONS OF BE3-1)( IONS WITH HE ATOMS BELOW 10 KEV AMU()

Cross sections of electron-capture processes are calculated by using a molecular-state expansion method in collisions of Be3+ ions with heli um atoms. Semiclassical and quantum-mechanical close-coupling equation s with ten molecular channels for the former and with three channels f or the latter are solved numerically at collision energies from 60 eV amu(-1) to 10 keV amu(-1) and from 10(-1) meV amu(-1) to 60 eV amu(-1) , respectively, to obtain scattering amplitude. The total cross sectio ns for the tripler Be2+ ion formation have a broad maximum at about E = 100 eV amu(-1) and decrease below, reaching a minimum around 5 eV am u(-1). But they begin to increase again below 5 eV amu(-1). At collisi on energies lower than 5 eV amu(-1) the contribution of the Be2+(1s2p) state to the electron-capture process is found to be larger than that of the Be2+(1s2s) state, but at intermediate collision;energies betwe en 5 eV amu(-1) and 10 keV amu(-1) the order of the contributions from these two states reverses. The total cross sections for the singlet B e2+ ion formation have a broad minimum at about E = 200 eV amu(-1) and they increase monotonically with decreasing collision energy. At most of the collision energies studied here, the contribution of the Be2+( 1s2s) state is found to be dominant. In both tripler and singlet Be2ion formation, at lower collision energies below 0.01 eV amu(-1), the cross sections begin to increase rapidly with decreasing collision ene rgy due to an orbiting effect, and several resonance-type peaks are al so seen. The position of these resonances can be assigned with the rov ibrational level of a quasimolecule formed during collision.