Subthermal photoproduct surface desorption distributions arising from excimer laser excitation of adsorbed trimethylaluminum

Excimer laser photolysis of adsorbed trimethylaluminum has been studied using a time of flight mass spectrometric technique. Methyl molecules are found to desorb with reasonable efficiency at 193 nm, but leave the surface with surprisingly small amounts of kinetic energy. Whereas, direct excitation of a single Al–C bond with a 6.4 eV photon would result in ∼3.5 eV of excess energy, only 0.025 eV is observed in translation experimentally. Maxwell–Boltzmann fits to these desorption distributions yield a temperature of ∼150 K even though desorption occurs from surfaces at room temperature. Possible interpretations of this result are discussed.

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