EFFECT OF ROTATION ON THE TRANSLATIONAL AND VIBRATIONAL-ENERGY DEPENDENCE OF THE DISSOCIATIVE ADSORPTION OF D(2) ON CU(111)

We have investigated the dependence on the rotational and vibrational states of the translational energy of D2(v,J) formed in recombinative desorption from Cu(111). These results provide information about the e ffect of rotational energy relative to that of vibrational and transla tional energy on the dissociative chemisorption of D2 on Cu(111). The range of rovibrational states measured includes rotational states J=0- 14 for vibrational state v=0, J=0-12 for v=1, and J=0-8 for v=2. D2 mo lecules were detected in a quantum-state-specific manner using three-p hoton resonance-enhanced multiphoton ionization (2 + 1 REMPI). Kinetic energies of desorbed molecules were obtained by measuring the flight time of D2+ ions in a field-free region. The mean kinetic energies det ermined from these measurements depend strongly on the rotational and vibrational states. Analyzing these results using the principle of det ailed balance confirms previous observations that vibrational energy i s effective, though not as effective as translational energy, in promo ting adsorption. Rotational motion is found to hinder adsorption for l ow rotational states (J < 5) and enhance adsorption for high rotationa l states (J > 5). Even for high J states, however, rotational energy i s less effective than either vibrational energy, which is 30%-70% more effective than rotational energy, or translational energy, which is 2 .5-3 times more effective than rotational energy in promoting adsorpti on. The measured internal state distributions for the rovibrational st ates listed above are consistent with the observed dependence of the k inetic energy of the desorbed molecules with the rotational state. In addition, the analysis performed yields the dependence of the adsorpti on probability on kinetic energy separately for each rovibrational sta te. These functions have very similar sigmoidal shapes for all states examined. Changing the quantum state is primarily associated with a sh ift in the position, or threshold energy, for the curves. The level at which these functions saturate or level off at high energy is indepen dent of rotational state but varies nonmonotonically with the vibratio nal state.