Hot atom

Abstract: We study the dynamics of transient hot H atoms on Pd(100) that originated from dissociative adsorption of H2. The methodology developed here, denoted AIMDEF, consists of ab initio molecular dynamics simulations that include a friction force to account for the energy transfer to the electronic system. We find that the excitation of electron-hole pairs is the main channel for energy dissipation, which happens at a rate that is five times faster than energy transfer into Pd lattice motion. Our results show that electronic excitations may constitute the dominant dissipation channel in the relaxation of hot atoms on surfaces.

Abstract: Analytical expressions are presented for the collision energy distribution and its width in hot atom reactions. These expressions are adapted from those derived previously by Chantry, for the related context of ion-molecule reactions. Although the spread in the collision energy distribution arises solely from the thermal motions of the reagents, its width exceeds the average thermal energies of the reagents, often substantially.

Abstract: Excitation functions for the various product channels in reactions of hot 18F atoms with ground‐state HD are calculated using the Monte Carlo quasiclassical trajectory technique and an optimized semi‐empirical potential energy surface. The production of H18F and D18F and dissociation into 18F+H+D are reported as a function of the center‐of‐mass collision energy over the range 0.1–65.0 eV. The calculated excitation functions for H18F and D18F cross at ∼ 7 eV indicating an inversion in the intramolecular isotope effect with increasing collision energy. Features of these excitation functions and the calculated product energy distributions are discussed in terms of simple mechanistic models. The trajectory results, on the average, correlate well with the predictions of the spectator stripping model from epithermal collision energies up to the limiting energy where this model would lead only to dissociation. The high‐energy tail of the abstraction excitation functions, however, is shown to be attributable to a...