Photoreaction dynamics of CH3I multilayers on GaAs(1 1 0): REMPI probing of the CH3 umbrella mode

The UV photodissociation dynamics of CH3I multilayers on GaAs(1 1 0) are studied using 2 + 1 resonant enhanced multiphoton ionization (REMPI) detection of the CH3 ν2 umbrella vibrational mode. The vibrational distribution formed appears much colder than the distribution resulting from gas-phase photodissociation of CH3I. Measurements of the surface reaction cross-section versus photon exposure and time-of-flight (TOF) studies of the CH3 translational energy suggest that the colder temperature is attributable to dissociative electron attachment (DEA) by photoemitted substrate electrons.