CHEMISORBED-MOLECULE POTENTIAL-ENERGY SURFACES AND DIET PROCESSES

We report the use of the local-density approximation, with and without gradient corrections, for the calculation of ground-state potential energy surfaces (PESs) for chemisorbed molecules. We focus on chemisorbed NO and ammonia on Pd(111) and compare our results with the latest experimental information. We then turn to two aspects of excited-stare PESs. First, we compare first-principles calculations of the forces on an ammonia ion as a function of distance from the surface. We find that the image-charge model fails significantly at distances which are the most relevant for dynamics, closer than similar to 3 Angstrom, and discuss reasons for the failure. We then summarize a purely electronic adiabatic model of the molecule-surface bond and use empirical parameters to estimate hot carrier-produced excited states of chemisorbed NO. We find multiple PESs and a novel interpretation of the pi* resonance, seen in inverse photoemission.