Angular-resolved time-of-flight measurements have been made of the photofragmentation of ${\mathrm{CH}}_3$Br adsorbed on GaAs(110). The results show two distinct angular lobes in the plane defined by the surface normal and the [01] direction, each with a characteristic threshold and fragment kinetic energy. The results are interpreted as originating from dissociative electron attachment of adsorbed ${\mathrm{CH}}_3$Br electrons which are supplied by either hot electrons (those excited above the conduction band minimum) in one direction or thermal electrons (those at the CBM) in the other.

• Received 14 September 1993

DOI:https://doi.org/10.1103/PhysRevLett.72.3068