THEORETICAL AND EXPERIMENTAL-STUDY OF N- (D-1) FORMATION IN NITROGEN COLLISIONS WITH A METAL-SURFACE

The dynamics of nitrogen collisions with metals partially covered by a lkali atoms is studied both experimentally and theoretically. Our atte ntion focuses on the formation of N-(D-1) metastable ions and their in teraction with the surface. We present the electron energy spectra ind uced by slow collisions of N+ ions with partially cesiated Pd(lll) sur faces under grazing incidence, These spectra display, as a function of Cs coverage, a sharp feature which is due to the autodetachment of N- (2p(4), D-1) to the N(2p(3), S-4) ground state. Our calculations, perf ormed with the coupled angular mode (CAM) method on the basis of the r esonant electron exchange between the nitrogen atom in stares of the 2 p(3) configuration and the metal surface, consistently explain how neg ative ions formed close to the surface can survive against electron lo ss to the metal during the outgoing trajectory and can later decay as free ions. In order to understand the alkali coverage dependence of th e N-(D-1)-N(S-4) peak intensity, the local character of the nitrogen i nteraction with the surface partially covered by adsorbate atoms has b een taken into account. (C) 1997 Elsevier Science B.V.