Simulation of the surface reaction of D-2 on a sulfur covered Pd(100) surface

Measurements of the rotational alignment of D-2 (J = 8) desorbing from Pd(100) show a significant dependence on the sulfur coverage. Molecules desorbing from clean palladium show a low rotational alignment of A(0)((2)) = +0.07, those from c(2 x 2) S/Pd(100) an alignment of A(0)((2)) = + 0.60. At all coverages a helicopter type of motion prevails. We have developed different models to describe the dependence of the rotational alignment on the sulfur coverage. Using Monte Carlo simulations the relative abundances of different reaction sites are calculated. These abundances and the m(J) population distributions for clean and sulfur influenced sites are used to model the behaviour for the rotational alignment at different S coverage. It is shown that at low coverages the reactions occur dominantly at bridge sites while at high S coverage hollow sites become important.