Extension of the Electron-Promotion Model to Asymmetric Atomic Collisions

The electron-promotion model is extended to include asymmetric atomic collisions. Diabatic correlations are made between the limits of united and separated atoms. The effects of core penetration are taken into account. The model is especially applicable to the case of inner-shell promotion. The promotion model agrees with the results of Specht, which show that promotion of electrons occurs when an energy level of one atom matches that of another. A detailed discussion of $L$-shell excitation is given. The model accounts in detail for the subshell-excitation effects and lack of reciprocity found between target and projectile by Kavanagh et al. The effects of outer-shell vacancies are felt in inner-shell excitation through the opening or closing of exit channels. In particular, the "solid effect" opens channels leading to outer-shell orbitals of the projectile. The Kessel model is applied to $L$-shell excitations in asymmetric collisions. The possibility of exciting both collision partners with nearly matching levels is taken into account. Two parameters are needed to fit the total cross section for excitation as a function of atomic number: the critical internuclear distance for a given pair of atoms and the effective range over which the promotion takes place. The parameters needed to fit the total-cross-section data of Cu on targets of different $Z$, taken by Kavanagh et al., agree with the differential-energy-loss and x-ray data, obtained by Fastrup et al., and by Saris, from different atoms scattered by atomic argon targets.