CORE-LEVEL SPECTROSCOPY STUDY OF N-2 ADSORBED ON (2X2)K GRAPHITE/

We report a study of N-2/(2 x 2)K/graphite at 25 K using X-ray photoem ission, X-ray absorption (XAS), ultraviolet photoemission, autoionizat ion and Auger spectroscopies. At this temperature me found that N-2 ph ysisorbs. Comparisons with the physisorbed system, N-2/graphite, revea l the role played by the alkali. The molecular coverage corresponding to saturation of the first monolayer is reduced drastically by the pre sence of potassium. Another dramatic effect induced by the potassium i s the very high binding energy of the N1s level due to a potassium-ind uced change of the work function and to a less efficient image charge screening. On the other hand. XAS, autoionization and Auger data show that in the core excited state the molecule increases its interaction with the substrate to the extent that the adsorbed potassium facilitat es charge transfer to neutral core-excited N-2. This is manifested by the appearance of a new type of final state in the autoionization. (C) 1998 Elsevier Science B.V. All rights reserved.