Model Hamiltonian for the interaction of NO with the Au(111) surface.

We have constructed a model Hamiltonian to describe the interaction of a nitric oxide (NO) molecule with a Au(111) surface. The diagonal elements of the 2x2 Hamiltonian matrix represent the diabatic potential energy surfaces corresponding to the neutral and negative-ion states of the molecule. A position-dependent off-diagonal element controls the extent of mixing of the two diabatic states. The parameters of the Hamiltonian matrix were determined from ground-state density functional theory calculations, both in the absence and presence of a small applied electric field to perturb the extent of charge transfer to the molecule. The resulting model Hamiltonian satisfactorily reproduces the ab initio results, and scattering simulations of the incident translational energy dependence of trapping probability and final rotational energy of NO agree quite well with experiment. The explicit incorporation of neutral and ionic configurations should serve as a realistic and practical platform for elucidating the importance of charge transfer and nonadiabatic effects at metal surfaces, as well as provide a useful testing ground for the development of theories of nonadiabatic dynamics.