Highly Rotationally Excited N2 Reveals Transition-State Character in the Thermal Decomposition of N2O on Pd(110)

We employ time-slice and velocity map ion imaging methodsto explorethe quantum-state resolved dynamics in thermal N2O decompositionon Pd(110). We observe two reaction channels: a thermal channel thatis ascribed to N-2 products initially trapped at surfacedefects and a hyperthermal channel involving a direct release of N-2 to the gas phase from N2O adsorbed on bridge sitesoriented along the [001] azimuth. The hyperthermal N-2 ishighly rotationally excited up to J = 52 (v '' = 0) with a large average translational energyof 0.62 eV. Between 35 and 79% of the estimated barrier energy (1.5eV) released upon dissociation of the transition state (TS) is takenup by the desorbed hyperthermal N-2. The observed attributesof the hyperthermal channel are interpreted by post-transition-stateclassical trajectories on a density functional theory-based high-dimensionalpotential energy surface. The energy disposal pattern is rationalizedby the sudden vector projection model, which attributes to uniquefeatures of the TS. Applying detailed balance, we predict that inthe reverse Eley-Rideal reaction, both N-2 translationaland rotational excitation promote N2O formation.

Automated summary

We employed time-slice and velocity map ion imaging methods to investigate the dynamics of thermal N2O decomposition on Pd(110) at the quantum-state resolved level. Two reaction channels were observed: a thermal channel involving N-2 products initially trapped at surface defects, and a hyperthermal channel where N-2 is released directly to the gas phase from N2O adsorbed on bridge sites. The hyperthermal N-2 exhibited high rotational excitation and significant translational energy, with a considerable portion of the energy released during dissociation being taken up by the desorbed N-2. The characteristics of the hyperthermal channel were explained using classical trajectories on a high-dimensional potential energy surface and the sudden vector projection model.