Inverted Cusps in Electron Spectra near Zero Velocity in an Attractive Coulomb Field

Abstract

An inverted cusp in the near-zero-velocity electron-loss spectrum for a $2p \mathrm{}(m=0\mathrm{})\mathrm{}$ initial state is predicted for an attractive final-state Coulomb interaction. The dip occurs in the singly differential cross section $\frac{d\sigma }{d{v}_e}$, calculated in Born approximation, at $v_e=v_P$, where the electron velocity $v_e$ matches the projectile velocity $v_P$ and where the familiar cusp normally appears. The dip becomes more pronounced with increasing projectile velocities $v_P\to \infty$. Its existence is traced to the odd ${\Pi }_z$ parity of the initial state.