  An exact solution of the time-dependent Dirac equation for ionization and
pair production induced by ultrarelativistic heavy ion collisions is presented.
Exact transition probabilities, equivalent to those that would be obtained in
an untruncated basis coupled channels calculation, are presented. Exact
bound-electron positron pair production probabilities are calculated to be
mostly smaller than those calculated with the same potential in perturbation
theory at impact parameters small enough for differences to occur.
