Simulating Highly Activated Sticking of H₂ on Al(110): Quantum versus Quasi-Classical Dynamics

Area of Science:

• Surface science
• Quantum mechanics
• Computational chemistry

Background:

• Investigating the sticking of hydrogen molecules (H2) on aluminum surfaces (Al(110)) is crucial for understanding surface reactions.
• Molecular beam experiments provide valuable data for validating theoretical models of gas-surface interactions.

Purpose of the Study:

• To quantify the significance of quantum effects on H2 sticking on Al(110).
• To compare quantum dynamics (QD) calculations with quasi-classical trajectory (QCT) methods under conditions relevant to molecular beam experiments.

Main Methods:

• Utilized a computational model allowing motion in six molecular degrees of freedom.
• Employed a potential energy surface with a minimum barrier height determined by quantum Monte Carlo methods.
• Performed both QCT and QD calculations, with QD benefiting from Monte Carlo averaging for reduced computational cost.

Main Results:

• The QD sticking probability curve is shifted to lower energies (0.05–0.21 kcal/mol) compared to the QCT curve.
• This energy shift is most pronounced at lower incident energies.
• Quantum effects were found to have a limited influence on the overall sticking probability.

Conclusions:

• Quantum effects play a small role in H2 sticking on Al(110) under the studied conditions.
• The findings suggest that QCT methods may be sufficient for evaluating electronic structure methods in this system.
• This has implications for the standard procedures comparing theoretical calculations with molecular beam experimental data.