Dissipative effects in the dynamics of N(2) on tungsten surfaces.

The role of electron-hole pair excitations in the dynamics of N(2) on W(100) and W(110) is evaluated using a theoretical model that accounts for the six-dimensionality of the problem in the whole calculation. The six-dimensional potential energy surface is determined in each case from an extensive grid of energies calculated with density functional theory. Dissipative effects due to electron-hole pair excitations are introduced in the classical dynamics equations through a friction force. Corresponding electron friction coefficients are calculated for each atom in the molecule with density functional theory in a local density approximation. Our results show that electronic friction plays a very minor role in the dissociative dynamics of N(2) in both tungsten faces. A similar conclusion is reached when we calculate the energy lost by the reflecting molecules.