Coverage- and Isotope-Dependent Langmuir-Rideal/Eley-Rideal and Hot-Atom Reaction Dynamics of H(D) with D(H)-Covered Pt(100): Quasiclassical Molecular Dynamics Simulations.

Hydrogen-isotope abstraction on platinum surfaces is a key elementary process in heterogeneous catalysis and hydrogen-related surface chemistry. In this work, coverage- and isotope-dependent reaction dynamics of H or D atoms impinging on D- or H-covered Pt(100) surfaces were investigated using quasiclassical molecular dynamics simulations with a flexible Pt slab at a fixed low incidence energy of 0.07 eV. The adsorbate coverage was varied from 0.18 to 0.80 monolayers (ML). Hydrogen isotope-Pt interactions were described using an adjusted London-Eyring-Polanyi-Sato potential, whereas the Pt substrate was represented by a many-body embedded-atom potential, enabling explicit lattice motion and energy transfer. Five outcome channels were quantified: HD formation, H2/D2 formation, surface sticking, below-top-layer penetration, and inelastic scattering. HD formation was the dominant reactive pathway and increased monotonically with coverage, whereas the total nonreactive probability decreased as the adsorbate layer became denser. Early HD products were associated with Langmuir-Rideal/Eley-Rideal and short-time hot-atom pathways, whereas delayed HD formation and H2/D2 production proceeded through longer-time hot-atom motion. Below-top-layer penetration was consistently more probable than surface sticking. D-on-H collisions produced higher HD probabilities than H-on-D collisions; this ordering is interpreted as an integrated isotope-dependent trajectory effect involving projectile momentum and speed, dynamical steering, adsorbate zero-point energies, and energy exchange with the adsorbate layer and Pt lattice. All conclusions are restricted to the explicitly simulated 0.18-0.80 ML intervsal. These results provide a surface-specific picture of how coverage, isotope mass, lattice flexibility, and near-surface accessibility jointly control low-energy hydrogen-isotope abstraction dynamics on Pt(100).