ELECTRON-EMISSION IN SLOW COLLISIONS OF HE PROJECTILES (HE-ASTERISK, HE-SURFACES AND LIF-SURFACES(, HE++) WITH LI)

We report the spectra of the electrons emitted in slow collisions of H e+ (50 eV) and He++ (100 eV) ions with a Li covered W(110) surface and with LiF films grown on Li/W(110). The preparation of the surfaces wa s made under in situ control of the metastable impact electron spectro scopy (MIES). The interpretation of the spectra is made on the basis o f simulated electron spectra: For collisions with Li/W(110) the ion in duced electron spectra are mainly due to Auger processes of the projec tiles after their resonant capture of electrons from the surface. Both Auger deexcitation and intra-atomic Auger processes, such as the auto detachment of He-- (1s2s(2)) and the autoionization of the ''hollow a toms'' He-* (2/2l') (l,l'=0, 1), are observed. For collisions with Li F films the neutralization of the projectiles takes place mostly by Au ger capture processes involving two electrons from the surface. The re sonant capture of an electron by the He++ into He-+ (n=2) state still occurs, but is weak. The formation of ''hollow atoms'' does not take place in front of dense LiF films. There are some indications that the quasi-resonant electron transfer involving F 2s electrons plays also a role in the interaction of He++ with the surface.