Vibrational relaxation of H-2 (upsilon = 1, J = 1) on Pd(111)

We have observed the relaxation of H-2 from the rovibrational state (v = 1, J = 1) into (v = 0, J = 5, and J = 7) upon scattering from Pd(lll). The relaxation probability is 0.04 +/- 0.01 into J = 5 and 0.03 +/- 0.01 into J = 7. Relaxation does not occur when the surface is saturated with H atoms at low temperature. Furthermore, relaxation occurs with significant loss of vibrational energy, 50-120 meV, to the substrate. The relaxation mechanism is most likely electronically nonadiabatic. The survival probability of the incident H-2 (v = 1, J = 1) is 0.05 +/- 0.01 for a clean surface, but nearly unity for an H-saturated surface.