Molecular Wave Functions and Inelastic Atomic Collisions

A theoretical interpretation is given of inelastic atomic collisions, especially violent cases where the atomic electron shells deeply interpenetrate. The basis set consists of a product of single-particle, hydrogen-molecular-ion orbital wave functions. The occurrence of large energy losses at critical internuclear distances can be seen as a result of the promotion of inner-shell electrons predicted by molecular-orbital (MO) theory. Energy losses, multiple ionization, and fast-electron ejection happen as a result of transitions between MO single-particle energy levels at crossings. A list is given of the mechanisms which cause an avoidance of diabatic crossings. After the collision, the atoms are left in narrow, discrete states with several electrons simultaneously, highly excited. This type of excitation occurs in heavy-particle collisions or in nuclear fission, but not in photon or electron bombardment. The presence of fast electrons at definite energies is seen as a unique prediction of the present model. The lack of correlation between the charge states of the separating atoms after the collision is seen to result from the weakness of correlation energy among electrons in highly excited, outer shells. The consistency of the MO model with the details of energy losses, fast-electron spectra, and positions of critical internuclear distances indicates the insufficiency of purely statistical models and the lack of necessity of the assumption of plasma oscillations or other ad hoc mechanisms. A noteworthy feature of this analysis is that the Born-Oppenheimer approximation has been extended to collisions which involve nuclear kinetic energies of several hundred kV.