Alignment and impact angular dependence to O₂ sticking and dissociation on Pt(111) and close-packed steps

Area of Science:

• Surface science
• Chemical kinetics
• Molecular dynamics

Background:

• Oxygen interaction with platinum surfaces is a key model system for understanding reaction mechanisms.
• Accurate theoretical descriptions require benchmarking against experimental data on surface structure influences.

Purpose of the Study:

• To measure initial sticking probabilities of O2 on Pt(111) and vicinal surfaces.
• To investigate the effect of molecular orientation (helicoptering, cartwheeling) on sticking.
• To understand how surface structure impacts O2 molecule dynamics.

Main Methods:

• Utilizing state-selected and rotationally-aligned O2 molecules.
• Measuring absolute initial sticking probabilities.
• Comparing sticking on flat Pt(111) versus stepped vicinal surfaces.

Main Results:

• Sticking probabilities varied significantly with molecular orientation for Pt(111).
• Vicinal surfaces showed higher reactivity and less dependence on molecular alignment.
• Highest sticking probabilities occurred at low incident energies for incidence into step facets.

Conclusions:

• Normal energy scaling appears valid for various molecular orientations.
• Vicinal surfaces exhibit complex angular dependencies and enhanced reactivity.
• Scattering into physisorbed states likely precedes chemisorption over a broad angular range.