Trapping-desorption and direct-inelastic scattering of HCl from MgO(100)

A molecular beam of hyperthermal HCl (J=0) impinges on a MgO(100) surface and the scattered HCl is probed state-selectively by using multiphoton ionization. Two regimes are identified. At incident energies of 0.54 and 0.90 eV, scattering is predominantly direct-inelastic, whereas at an incident energy of 0.11 eV, HCl is predominantly trapped and subsequently desorbs. For example, at 0.11 eV, the angular distribution of the HCl product is cosine-like, whereas at 0.54 and 0.90 eV, the scattered HCl is observed to peak near the specular angle.