Classical Molecule–Surface Scattering in a Quantum Spirit: Application to H2/Pd(111) Nonactivated Sticking

The semiclassical initial value representation is used to derive a simple expression for the sticking probability in nonactivated dissociative chemisorptions of diatomic molecules. This expression, whose calculation requires only the running of classical trajectories, takes into account two quantum mechanical effects: (i) the vibrational quantization of reflected molecules and (ii) a diffraction-mediated trapping of part of the incoming wave. For the title process, our approach leads to predictions in much better agreement with quantum scattering results than the standard quasiclassical trajectory method for a similar computational effort. Moreover, we provide a simple semiclassical explanation of the nonmonotonic dependence of the quantum sticking probability on the collision energy. In principle, the present approach should be applicable to nonactivated dissociative chemisorptions of polyatomic species for which quantum scattering calculations are generally beyond reach.