Femtosecond laser induced desorption of H_2, D_2, and HD from Ru(0001): Dynamical promotion and suppression studied with ab initio molecular dynamics with electronic friction

摘要

We perform ab initio molecular dynamics simulations to study the femtosecond laser induced desorption ofH_2, D_2, and HD from a H:D-saturated Ru(0001) surface. To this aim we have extended the ab initio moleculardynamics with electronic friction (AIMDEF) scheme to include a random force that is a function of a timedependentelectronic temperature. The latter characterizes the action of the ultrashort laser pulse according to atwo temperature model. This allows us to perform multidimensional, hot-electron driven reaction dynamics andinvestigate the dependence of the desorption yields on the relative H:D isotope concentration on the surface. OurAIMDEF simulations show that the desorption process takes place in the presence of a heated adsorbate systemthat clearly influences the desorption dynamics. The heating of the adsorbate system is more (less) pronouncedthe larger is the concentration of the lighter (heavier) isotope. As a result, we conclude that the presence of H onthe surface favors the desorption of molecules, whereas the presence of D hampers it, in agreement with previousexperimental observations in which the phenomenon of “dynamical promotion” of a surface reaction had beenpostulated [Denzler et al., Phys. Rev. Lett. 91, 226102 (2003)].