Excitation processes in slow K+--He, Ne, Ar, H2, N2 and Na+--He collisions

Quasimolecular features of excitation processes in K+--He, Ne, Ar, H2, N2 and Na+--He collisions were investigated by measuring the cross sections for the emission of the resonance lines of potassium (lambda = 766.5 and 769.9 nm), sodium (lambda = 589 and 589.6 nm), and helium (lambda = 584 nm) atoms at ion energies in the range 0.5--10 keV. In Na+--He collisions, the resonance-line excitation functions obtained for sodium and helium atoms exhibit oscillations that are in antiphase and are due to phase interference between the quasimolecular states of the system of colliding particles. Experimental data on K+--Ar collisions are interpreted in terms of schematic correlation diagrams for molecular orbitals. The excitation mechanisms for K+--N2 and K+--Ar have beenfound to be similar, and this leads to the conclusion that the quasimolecular model used for the ion-atom case is also valid for the ion-molecule case. It is shown that the excitation of the 4p-state of the potassium atom in the K+--Ar case is due to a Landau-Zener type of interaction in the region of the quasicrossing of (KAr)+ terms. Analysis of the excitation of this state in K+--N2 collisions also shows that the capture of an electron into the excited 4p-state of the potassium atom is due to a nonadiabatic transition in the region of quasicrossing of energy terms of the same symmetry