Electronically excited photodissociation and desorption of molecules on surfaces

CH212 molecules adsorbed on AI2O3 and A1 surfaces are used as a model system for studying the photofragmentation and desorption processes involving electronic excitation of the adsorbate. The molecules are promoted into an antibonding state with a pulsed 308-nm laser and the desorption behavior is monitored by time-of-flight mass spectrometry. The system is characterized by x-ray photoelectron spectroscopy, Auger electron spectroscopy, and thermal desorption spectroscopy. The desorption yields as well as the mass and the kinetic energy distributions are determined as a function of surface coverage and laser fluence. The results reveal the electronic, thermal, and ‘explosive” desorption characteristics depending on both the gaseous exposure and the laser irradiation conditions. © 1987, American Vacuum Society. All rights reserved.