VIBRATIONAL RELAXATION OF H2 (V = 1, J = 1) ON PD(111)
We have observed the relaxation of H{sub 2 } from the rovibrational state (v=1,J=1) into (v=0, J=5, and J=7) upon scattering from Pd(111). The relaxation probability is 0.04{plus_minus}0.01 into J=5 and 0.03{plus_minus}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{endash}120 meV, to the substrate. The relaxation mechanism is most likely electronically nonadiabatic. The survival probability of the incident H{sub 2} (v=1,J=1) is 0.05{plus_minus}0.01 for a clean surface, but nearly unity for an H-saturated surface. {copyright} {ital 1997} {ital The American Physical Society}