Transition Probability of Neutralization Process of +2 Ion Scattered on a Metal Surface

抄録

We examine the transition probability in the neutralizing process of +2 ion such as Be⁺², Ca⁺² and Ba⁺² through the electron transfer between the ion and a metal surface, using an impurity Anderson Hamiltonian. Within second order perturbation theory with respect to the transfer integral, an analytical expression of the transition probability is derived and numerically calculated. From the numerical results, the neutralization process of +2 ion on the metal surface seems to occur more easily with decreasing the atomic number of an ion. The transition probability depends on not only the initial kinetic energy of the moving ion but also its species of ions. In addition, the plot of the transition probability as a function of the initial velocity of ions theoretically suggests the presence of an optimized initial velocity for the neutralization process. From the contour map of the transition probability plotted as functions of energy difference E_a−E_F (E_a: energy of localized electron, E_F: Fermi energy) and intra Coulomb potential U, we can see that the neutralization process of Be⁺² easily occurs in the range of E_a−E_F being from −0.8 eV to −1.2 eV and U being from 0.5 eV to 0.7 eV, when the initial kinetic energy is 100 eV. The plot for various U shows that the transition probability almost vanishes when U=0.0 eV. This seemingly contradictory result arises from the fact that for small U the transition matrix element cancels in the second-order process as a result of the energy conservation.