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It is shown that alkali adatoms coadsorbed in the presence of adsorbed hydrogen on Ni(111) can cause a large increase in the cross section for H+ emission during electron stimulated desorption. This phenomenon was investigated using the digital ESDIAD (electron stimulated desorption ion angular distribution) technique as well as by temperature programmed desorption (TPD). H+ ions produced by electron impact on alkali–hydrogen complexes are ejected in sharp normally oriented ion angular distributions. The sensitization of the H(a)→e−H+ process occurs with Li, Na, and K but not as strongly with Rb and Cs. Attractive interactions exist in the adsorbed layer between the hydrogen and the alkali adatoms. A model is discussed involving the formation of ‘‘alkali–hydride‐like’’ surface complexes, with Hδ− located on top of alkali atom sites. |
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