Rotational effects in six-dimensional quantum dynamics for reaction of H-2on Cu(100)

We present results of six-dimensional (6D) quantum wave-packet calculations for the dissociative adsorption of (v = 0,j = 4,m(j)) H-2 on Cu(100). The potential-energy surface is a fit to points calculated using density-functi onal theory (DFT), with the generalized gradient approximation (GGA), and a slab representation for the surface. New aspects of the methodology we use to adapt the wave function to the symmetry of the surface, which relate to calculations for initial rotational states with odd m(j) (the magnetic qua ntum number), are explained. Invoking detailed balance, we calculate the qu adrupole alignment for H-2 as it would be measured in an associative desorp tion experiment. The reaction of the helicopter (v = O,j = 4,m(j) = 4) stat e is preferred over that of the ( v = 0,j = 4,m(j) = 0) cartwheel state for all but the lowest collision energies considered here. The energy dependen ce of the quadrupole alignment that we predict for (v = 0,j =4) H-2 desorbi ng from Cu(100) is in good qualitative agreement with velocity-resolved ass ociative desorption experiments for D-2 + Cu(111). The vibrational excitati on probability P(v = 0,j --> v = 1) is much larger for j = 4 than for j = 0 , and the m(j)-dependence of P(v = 0,j = 4,m(j) --> v = 1) is markedly diff erent from that of the initial-state-resolved reaction probability. For all but the highest collision energies, vibrational excitation from the (v = 0 ,j = 4) state is accompanied by loss of rotational energy, in agreement wit h results of molecular beam experiments on scattering of H-2 and D-2 from C u(111). (C) 1999 American Institute of Physics.