The photochemical and thermal desorption behavior of CH2I2 adsorbed on an Al film has been studied by X-ray photoemission, thermal desorption and time-of-flight mass spectrometry with both UV and visible lasers. The products and the energetics of surface reactions are determined as functions of surface coverage and laser fluence. It is found that CH2 radicals and C2H4 molecules can be produced and desorbed from the surface when the adsorbate is electronically excited. In addition, laser-induced transient heating of Al substrate can lead to a decomposition reaction very different from the conventional thermal desorption. © 1989.