Evaluation of exchange matrix elements with momentum transfer for ion-atom collisions

A suitable technique has been presented for the evaluation of exchange matrix elements with the momentum transfer term in the impact-parameter formulation. All these exchange matrix elements can be obtained with the help of only two functions, S and its derivative S', which are simple one-dimensional integrals containing exponential functions. We give an efficient and easily programmable procedure for quick and accurate evaluation of these functions. The present method of evaluation of the exchange matrix elements is very economic from the computational point of view for higher excited states. The technique has been verified by its application to the calculation of the interaction and overlap integrals occurring in proton-hydrogen-atom collisions. The same integrals have been computed by a method developed by McCarroll and the results of calculations by both the methods are found to be in excellent agreement. (author)