Rotational and vibrational population of D2 desorbing from sulfur-covered Pd(100) -: art. no. 115405

We report rovibrational populations of D-2 desorbing recombinatively from sulfur-covered Pd(100). The palladium surface is poisoned with an ordered c(2x2) overlayer corresponding to a coverage of Theta(S)approximate to0.5 ML. Desorbing D-2 molecules are detected with (1+1(')) REMPI via various B(1)Sigma(u)(+)<--X(1)Sigma(g)(+) Lyman bands using tunable vacuum ultraviolet laser radiation for the excitation step. Rotational quantum states J(')=0-12 in the vibrational ground and J(')=0 to 8 in the first vibrational excited state are measured. Experiments are performed for surface temperatures in the range from T-S=500-800 K. Rotational energies lower and vibrational energies higher than the corresponding surface temperature are observed. The vibrational energies are higher than those of molecules desorbing from a clean Pd surface. The experimental results are compared with quantum dynamical calculations for the desorption of H-2 from a p(2x2) sulfur-covered Pd(100) surface, based on a potential energy surface derived from density functional calculations. While the observed rotational cooling for molecules in the vibrational ground state is reproduced by the calculations, the vibrational effects are underestimated.