Ammonia and deuterated ammonia exhibit an anomalously large isotope effect in their relative yields and rotational spinning energy for electron-stimulated desorption from Pt(111). Quantum-resolved desorption measurements and ab initio, two-dimensional, potential energy calculations suggest that the desorbate undergoes a geometry change (molecular inversion) induced by the excited state. Inverted molecules deexcite to a repulsive hard wall potential and desorb. In general, multidimensional potential energy surfaces determine the dynamics of stimulated surface processes.

• Received 14 February 1994

DOI:https://doi.org/10.1103/PhysRevLett.72.3895