Triple-coincidence experiment to study the correlated electron emission in the collision-induced double electron loss of He−

Abstract

The double electron loss (DEL) from ${\mathrm{He}}^{\ensuremath{-}}$ has been investigated in collisions with He atoms at 300-keV impact energy and at electron energies that satisfy the cusp condition; i.e., the corresponding electron velocities match the projectile's velocity. In a time-of-flight experiment the energies of both electrons have been determined by detecting triple coincidences between the two electrons and the outgoing ${\mathrm{He}}^{+}$ ion. The coincidence yield shows a peak as a function of the electron energies at the expected cusp position, providing evidence for the existence of the two-electron cusp [L. Sarkadi and A. Orb\'an, Phys. Rev. Lett. 100, 133201 (2008)] in DEL. The observed energy distribution of the electron pairs is compared with the results of four-body classical trajectory Monte Carlo calculations carried out applying the soft-Coulomb potential approximation for the inclusion of the electron-electron interaction.