Activated Dissociation of H2 on Cu(001): The Role of Quantum Tunneling

TL;DR

This study theoretically investigates how quantum tunneling influences H2 dissociation on Cu(001), revealing significant tunneling effects at room temperature and below, and providing insights consistent with experimental observations.

Contribution

The paper introduces a first-principles analysis of quantum tunneling effects on H2 dissociation on Cu(001), highlighting the role of translational and vibrational motions in the process.

Findings

Quantum tunneling significantly affects dissociation rates at low temperatures.

The activation barrier is approximately 0.59 eV as determined by first-principles calculations.

Crossover from classical to quantum regime occurs at low temperatures.

Abstract

The activation and dissociation of H2 molecules on Cu(001) surface is studied theoretically. The activation barrier for the dissociation of H2 on Cu(001) is determined by first-principles calculations to be ~ 0.59 eV in height. Electron transfer from the substrate Cu to H2 plays a key role in the activation, breaking of the H-H bond and the formation of the Cu-H bonds. At around the critical height of bond breaking, two stationary states are identified, which correspond respectively to the molecular and dissociative state. Using the transfer matrix method, we are able to study the role of quantum tunneling in the dissociation process along the minimum energy pathway (MEP), which is found to be significant at room temperature and below. At given temperatures, the tunneling contributions from the translational and vibrational motions of H2 are quantified for the dissociation process. Within a wide range of temperatures, the effects of quantum tunneling on the effective barriers of dissociation and the rate constants are revealed. The deduced energetic parameters associated with thermal equilibrium and non-equilibrium (molecular beam) conditions are comparable with experimental data. In the low-temperature region, crossover from classical to quantum regime is identified.