| Attributs | Valeurs |
|---|
| type
| |
| Is Part Of
| |
| Subject
| |
| Title
| - Kinetics of NH Formation and Dissociation on Pt(111)
|
| has manifestation of work
| |
| related by
| |
| Author
| |
| Abstract
| - The kinetics of formation and dissociation of the NH species on the Pt(111) surface has been studiedexperimentally with time-resolved reflection absorption infrared spectroscopy (RAIRS) and theoretically withdensity functional theory (DFT). An intense and narrow peak at 3321 cm-1 due to the NH stretch vibrationcharacterizes the NH species. This RAIRS peak enables the NH coverage to be accurately measured as afunction of time during the formation and dissociation reactions. The experiment is performed by first preparinga well-ordered p(2 × 2)-N layer through oxydehydrogenation of NH3, then exposing the p(2 × 2)-N layer toH2 at low temperature. It is found that NH formation follows first-order kinetics, whereas the dissociationreaction follows second-order kinetics. Because NH is more stable on the surface than N and H, the dissociationrate is limited by the recombinative desorption of H2, which accounts for the observed reaction order. Theexperimental rate constants were compared with the corresponding theoretical values obtained with DFTusing a plane wave basis set and ultrasoft pseudopotentials. Rate constants were calculated based on the ratioof vibrational partition functions of the transition state and the reactants. From the DFT calculations, theactivation barrier for NH formation is found to increase strongly with increasing NH coverage. This mayresult in a compensation effect in the experimental parameters derived from an Arrhenius plot in which a lowapparent activation energy is compensated by a low pre-exponential factor. Although a semiclassical theoryindicates that quantum mechanical tunneling may play a role in the kinetics of NH formation, the observationof similar rates for NH and ND formation conclusively rules out any significant contribution from tunnelingto the rates.
|
| article type
| |
| is part of this journal
| |
