Fragmentation of molecular adsorbates by electron and ion bombardment: Methoxy chemistry on Al(111)

Abstract

(High resolution) electron energy loss spectroscopy [(HR)EELS] has been used successfully to provide direct spectroscopic evidence regarding details of the molecular fragmentation of methoxy (CH3O) on Al(111) caused by energetic electron and ion beams. Chemisorbed methoxy on Al(111) is produced by heating of adsorbed CH3OH. Irradiation of CH3O(a) by either energetic (∼300 eV) electrons or Ar+ ions results in C–O and C–H bond scission with simultaneous formation of Al–O and Al–C bonds. During electron stimulated desorption the CH3O(a) species undergo sequential fragmentation first to CHx groups that are captured by the surface and in the final decay process to adsorbed carbon. C–O bonds in CH3O(a) are depleted preferentially compared to C–H bonds in CHx(a) species. The electron induced sequential fragmentation of the parent CH3 group (from methoxy) to resultant CHx(a) occurs with an efficiency ∼3 orders of magnitude greater then the subsequent process of CHx(a) →C(a). Cross sections for various bond scission processes in electron and ion bombardment have been estimated.