Core-induced photofragmentation of acetonitrile adsorbed on Au(111) and Pt(111)

Photodissociation of acetonitrile (CH3CN) condensed, physisorbed on Au(111), and chemisorbed on Pt(111), has been studied at the C(1s) and N(1s) edges in H+ yield and/or in total positive ion yield. The H+ yield C(1s) absorption experiment on the condensed acetonitrile shows a selective fragmentation of the C–H bond at the C 1s→π*CH3 excitation, that is still observed when acetonitrile is physisorbed on Au(111) and chemisorbed on Pt(111). Transitions to the π*C≡N state give rise to unselective fragmentations, which are strongly quenched by charge transfer from the substrate when acetonitrile is chemisorbed on Pt(111). The π⊥*C≡N level that plunges into the Pt(111) is the most affected and vanishes in the total ion yield measurement. The quenching is weaker on the π∥*C≡N which is parallel to the surface, and thus is less hybridized with the metal than the π⊥*C≡N. For acetonitrile physisorbed on Au(111), the influence of the surface is limited to the quenching of the desorption of the heaviest outgoing fragments.