1s sigma molecular orbital ionisation in asymmetric ion-atom collisions by direct Coulomb interaction

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Abstract
Adiabatic perturbation theory is applied to the ionisation of the 1s sigma molecular orbital (MO) and extended to less adiabatic collisions by imposing an asymptotic matching with the semiclassical approximation. The transient molecular state wavefunction is modelled using the concept of an 'effective' charge for the colliding system. Through this procedure the transition amplitudes are evaluated simulating both the relaxation of the passive electrons and the modification of the active electron wavefunction, as well as their connection with the motion of the centre of charge during the collision. The direct Coulomb ionisation of the 1s sigma MO is calculated for projectiles following hyperbolic paths, in terms of this 'effective' charge, using the current-vector formalism. Comparison is made with a large amount of experimental data and good agreement is found.