Thirty years of MGR: How it came about, and what came of it

Starting from some personal recollections about the origins of the MGR model of electronically stimulated desorption, in particular on the MG side, I give a subjective view of the developments it initiated, the generalizations it allows, and the spin-offs it produced. The basic concept of the competition between the evolution of a repulsive excitation along its dissociation coordinate(s) and the quenching of that excitation by energy and/or charge exchange is stressed, which can also be characterized as interplay of localization and delocalization of the excitation. Some examples for recent extensions of the model which can explain novel, more detailed observations will be given. These include very recent observations in this laboratory of extremely high vibrational excitations in ESD-produced CO from group VIII metal surfaces, which can be readily understood on the basis of the MGR model applied to the internal (molecular) and external (adsorbate-substrate) coordinates in these systems.