MULTIPLE IONIZATION OF ATOMS AND MOLECULES IN COLLISIONS WITH FAST IONS - II - ION-MOLECULE COLLISIONS

An extended version of the statistical energy-deposition model is used for a description of multiple ionization of molecules by energetic io n impact. The energy transferred to the molecule during the collision is calculated as a function of the impact parameter within the local-e lectron-density approximation for a fixed molecular orientation. The f luctuating character of the deposited energy is taken into account by introducing a straggling of the energy transfer. For a given deposited energy the probability of multiple ionization of the molecule is assu med to be proportional to the volume of phase space available at the c onsidered ionization state. The total ionization cross sections obtain ed by integrating over impact parameters and averaging over all orient ations of the molecule, Sample calculations for collisions of He and F ions with N-2 and CO molecules are presented and compared with experi mental data. A dependence of the multiple ionization cross section on the molecular orientation is considered. A strong molecule alignment e ffect has been obtained in agreement with recent experimental findings . [S1050-2947(98)00702-1].