Isotopic effect for hydrogen atoms interacting with a cesiated surface

The interaction of deuterium atoms on a cesiated surface and the formation of hydrogen isotopologue molecules via the Eley–Rideal mechanism is studied using the computational set-up recently adopted in simulations of the same reactions for H atoms. The probability for scattering and adsorption processes on the surface as well as the mechanism underlying the reaction is shown for D atoms impinging on the surface in the same dynamical conditions previously used for H atoms. The isotopic effect in molecule formation is highlighted by considering the formation of D₂ and HD molecules; this latter is obtained by exchanging either the incoming or pre-adsorbed H atom with a D isotope. Collisional data have been determined for two different adsorption sites on the surface. The recombination probabilities and coefficients for D₂ and HD and the probabilities of other competitive surface processes have been determined. Internal states of isotopic molecules were solved and compared with those of H₂ molecules formed on the same surface showing that the heteronuclear molecules are vibrationally more excited. A strong isotope mass effect emerged in the collision of the D atom enhancing the probabilities for adsorption/desorption processes. Interestingly, a D atom impinging on the pre-adsorbed H atom on the surface increases the recombination probability, which remains low nonetheless. (paper)