Angular dependence of dissociation in steering dominated activated reaction

The angular dependence of dissociation has been explored using classical trajectory methods for model potential energy surfaces having wells into which molecules steer before dissociating. It was found that when the potential well is located at the surface site with the lowest dissociation barrier, the dissociation probability decreases with increasing angle of incidence due to shadowing effects. However when the well is moved before the site having the highest barrier, steering to that site dominates. In this case, the dissociation can increase with incidence angle due to molecular refraction onto the lowest dissociation barrier. For certain well depths we obtain almost no angular dependence to dissociation. These results are discussed with reference to experimental dissociation measurements for the O2/Al(1 1 1) and N2/W(1 1 0) systems, which exhibit non-monotonic and approximately zero angular dependence (so-called total energy scaling) respectively.