Theory of electron capture by fast projectiles scattered through large angles

A simple theory is presented for the process of electron capture when a fast incident projectile is scattered through large angles, i.e. greater than a few degrees. In this theory, the capture amplitude is shown to be proportional to the amplitude for ionisation of the target electron into a continuum state with velocity equal to the final projectile velocity. A particular feature of the model is the prediction of an enhanced capture probability, increasingly more pronounced with increasing collision velocity, when the projectile is scattered through a critical angle.