Photodesorption of Ammonia from GaAs(100) and Cu(111)
The laser-induced desorption of ammonia from GaAs(100)-(4*6) and Cu(111) has been studied using (2+1)-photon resonance enhanced multiphoton ionization (REMPI) as a state specific probe. A surprisingly marked isotope effect (NH₃/ND₃) in the photodesorption cross section of ammonia from GaAs(100) had indicated that internal degrees of freedom play a crucial role in the desorption dynamics. We find that NH₃ desorbs with a mean translational energy, , of 300K and 600K for GaAs(100) and Cu(111), resp. The av. extent of vibrational excitation is about 1000K. The rotational temps. are 520 and 170K. These results are interpreted in terms of a direct mechanism for NH₃ desorption in which a reaction path which initially follows the internal ν₂ coordinate and then bends towards desorption is dominating. A marked unequal population of the inversion symmetry doublet states is obsd.
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