Electron emission from temporary negative N −∗( 1D) ions formed in slow collisions of N + with insulator surfaces (LiF; CsI)

Abstract

The emission of electrons in slow collisions (50 to 500 eV) of N + ions with thin insulating films (LiF and CsI on tungsten) is reported. The electron spectra display a sharp feature which is due to the autodetachment of N −∗(2p 4; 1D) to the N 0)2p 3; 4S) ground state (on top of a smooth continuous background). In order to understand the dynamics of the formation of the temporary negative ion, the local character of the nitrogen interaction with the surface must be taken into account. The first step in the projectile-surface interaction is the resonant neutralization of the N + projectile into states of the N 0 2p 3 configuration, in particular into N ∗( 2D). The second step is the attachment of an additional surface electron to the nitrogen atom; this capture is mediated by the strong interaction between the temporary negative N −∗( 1D) ion and the hole in the surface anion (generated as the consequence of the electron transfer to the projectile).