ABOVE-SURFACE NEUTRALIZATION OF SLOW HIGHLY-CHARGED IONS IN FRONT OF IONIC-CRYSTALS

We present a theoretical analysis of the above-surface neutralization of highly charged ions in front of LiF. The study is based on the assu mption that the dominant electron transfer occurs in the classically a llowed region. Estimates of critical distances and corresponding quant um numbers for capture from an ionic crystal within the classical-over barrier (COB) model are presented, which differ considerably from corr esponding results for metals. The role of the dielectric response of L iF is investigated. In addition, classical-trajectory simulations are performed for a slow highly charged ion approaching an insulator. It i s shown that capture effectively begins similar to 3 a.u, closer to th e surface than estimated from the COB model. This correction can be in corporated into a modified COB model. The energy gain for grazing inci dence ions is obtained using a staircase model which includes the dece leration due to charge-up of the surface.