Recombinative desorption of H2 and D2 from Cu(110) and Cu(111): Determination of nonequilibrium rovibrational distributions

Rotational and vibrational state distributions have been determined for H2 and D2 recombinatively desorbing from clean Cu(110) and Cu(111) surfaces in ultra-high vacuum. A 2+1 resonance-enhanced multiphoton ionization technique is employed. Rotational distributions for both isotopes are found to be mildly non-Boltzmann and having mean rotational energies less than the surface temperature Ts and equal for both surfaces. The (v″=1)/(v″=0) vibrational population ratio for both H2 and D2, however, is ∼50 times greater than the value expected for an equilibrium ensemble at Ts for desorption from Cu(110) and ∼100 times greater from Cu(111).