ELECTRON-EMISSION FROM TEMPORARY NEGATIVE N-ASTERISK(D-1) IONS FORMEDIN SLOW COLLISIONS OF N+ WITH INSULATOR SURFACES (LIF CSI)

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 autodeta chment of N-(2p(4); D-1) to the N-0(2p(3); S-4) ground state (on top of a smooth continuous background). In order to understand the dynamic s of the formation of the temporary negative ion, the local character of the nitrogen interaction with the surface must be taken into accoun t. The first step in the projectile-surface interaction is the resonan t neutralization of the Nf projectile into states of the N(0)2p(3) con figuration, in particular into N(D-2). The second step is the attachm ent of an additional surface electron to the nitrogen atom; this captu re is mediated by the strong interaction between the temporary negativ e N-(D-1) ion and the hole in the surface anion (generated as the con sequence of the electron transfer to the projectile).