Scattering-theory approach to ammonia photodesorption from Cu(111)

A two-dimensional scattering theory approach is presented to describe photon- and electron-induced desorption of NH₃ and ND₃ from Cu(111). Similarly like in recent computer simulations, the relevant degrees of freedom are the distance between the surface and the center of mass of the molecule along the normal to the surface and the distance between the N atom and the plane of H or D atoms. The evolution of the molecule's wave packet on the excited electronic state potential is followed analytically and then a numerical integration of a set of close-coupled Schr\"odinger equations is used to compute the vibrational and kinetic-energy distribution of desorption products. Isotope effect is investigated in detail and a comparison with experimental and recent simulation data is made.