"Inverted" CO molecules on NaCl(100): a quantum mechanical study.

Area of Science:

• Surface science
• Physical chemistry
• Computational materials science

Background:

• Experimental observation of inverted (O-down) CO adsorbates on NaCl(100) after infrared vibrational excitation.
• Need for theoretical characterization of these CO species and their inversion dynamics.

Purpose of the Study:

• To theoretically characterize inverted CO adsorbates on NaCl(100) using density functional theory.
• To determine energy barriers and reaction pathways for CO inversion.
• To investigate the vibrational properties of CO on NaCl(100) at different coverages.

Main Methods:

• Periodic density functional theory (DFT) calculations.
• Quantum mechanical description of vibrations.
• Transition state theory (TST) for rate estimation.
• Solution of the time-independent nuclear Schrödinger equation for vibrational eigenstates.

Main Results:

• Coverage-independent CO inversion energies (approx. 0.08 eV) and classical activation energies for C-down to O-down isomerization (approx. 0.15 eV).
• Vanishingly small thermal rates for C-down to O-down isomerization at 22 K, but non-negligible rates for the reverse reaction.
• Identification of accidentally degenerate vibrational eigenstates below the barrier, localizing CO in C-down and O-down configurations.

Conclusions:

• The study provides a detailed theoretical understanding of CO inversion on NaCl(100).
• Low energy barriers support the experimental observation of O-down CO species.
• Vibrational analysis reveals localized states that facilitate the observed CO orientations.