Femtosecond near-infrared laser desorption of multilayer benzene on Pt{111}: spatial origin of hyperthermal desorption

The intense (10(12) W cm(-2), 800 nm) near-infrared laser desorption of benzene adsorbed on Pt{111} is reported. Velocity distributions are measured up to an adsorbate coverage of 20 monolayers. The velocity distributions reveal up to three distinct features: a hyperthermal feature with translational energy of 0.2 eV, a thermal feature and a subthermal feature. The translational energy of the hyperthermal feature is relatively independent of coverage and maintains constant desorption intensity from 4 to 20 ML. Experiments employing layered films of C6H6 and C6D6 reveal that the hyperthermal feature originates in the layers closest to the multilayer-vacuum interface. (C) 1999 Elsevier Science B.V. All rights reserved.