Hydrogen Recombination and Dimer Formation on Graphite from Ab Initio Molecular Dynamics Simulations

Area of Science:

• Astrochemistry
• Surface Science
• Chemical Physics

Background:

• Molecular hydrogen (H2) formation is crucial for the interstellar medium (ISM).
• The Eley-Rideal mechanism is a proposed pathway for H2 formation on dust grains.
• Understanding H2 formation on graphite is key to astrochemistry and plasma physics.

Purpose of the Study:

• Investigate Eley-Rideal H2 formation on graphite surfaces.
• Determine the energy range for H2 formation relevant to ISM and cold plasma experiments.
• Analyze projectile steering effects and dimer formation pathways.

Main Methods:

• Ab initio molecular dynamics simulations.
• Calculations of reaction cross sections.
• Analysis of ro-vibrational product populations.

Main Results:

• Projectile steering effects significantly inhibit dimer formation at low energies (0.02-1 eV).
• Efficient ortho and para dimer formation observed only at energies too high for ISM relevance.
• Simulated adsorbate configurations match experimental scanning tunneling microscopy observations.

Conclusions:

• The Eley-Rideal mechanism is unlikely to be a dominant pathway for H2 synthesis in the ISM under studied conditions.
• Computed data align well with experimental findings for H2 formation and surface interactions.
• This study refines our understanding of H2 formation on interstellar dust analogs.