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Abstract:
The photodesorption dynamics of ammonia from Cu(111) and GaAs(100)-(4 × 6) has been studied using (2 + 1) resonance-enhanced multiphoton ionization (REMPI) as a quantum-state-specific probe. Hyperthermal excitation of the v2 mode is observed for both substrates. Photodesorption from Cu is characterized by a marked underpopulation of antisymmetric v2 levels, whereas for NH3GaAs the population of the v2 mode follows Boltzmann statistics. The t systems also differ in the amount of rotational excitation and translational energy. The experimental results are discussed referring to a model which was developed recently to account for the large isotope effect in ammonia photodesorption. The model describes correctly the different quantum state distributions within the v2 manifold for the two systems.
