Resonant transfer and excitation by crystal channeling

A transition amplitude for resonant transfer and excitation (RTE) in a crystal channel is derived and compared with observations of Belkacem et al. [Phys. Rev. Lett. 64, 380 (1990)] of titanium ions channeled in a thin gold crystal. Using a one-dimensional tight-binding model of the gold lattice, the RTE cross section is shown to be proportional to the Compton profile of atomic gold multiplied by a crystal-structure factor, analogous to multislit interference of light with diffraction. It is suggested that Belkacem et al. observed a single (principal) maximum with a very narrow width determined by the crystal’s Fermi energy. It is found that the observed shift in the RTE peak, relative to that expected for a quasifree crystal electron, can be accounted for by a change in the Coulomb energy of the transferred electron caused by the highly charged ‘‘impurity’’ ion prior to transfer.