Nonadditive effects in ternary H2-cation-PAH systems

Area of Science:

• Computational Chemistry
• Quantum Chemistry
• Physical Chemistry

Background:

• Molecular hydrogen (H2) plays a crucial role in various chemical and physical processes.
• Understanding H2 interactions within complex systems is vital for fields ranging from materials science to astrophysics.
• Ternary complexes involving H2, cations, and polycyclic aromatic hydrocarbons (PAHs) are relevant to interstellar chemistry and gas storage.

Purpose of the Study:

• To investigate the binding energies of molecular hydrogen in ternary complexes with alkali cations (Li+, Na+) and PAHs.
• To quantify the nonadditive contributions to H2 stabilization energy in these systems.
• To elucidate the physical origins of nonadditive effects, particularly the role of induction.

Main Methods:

• State-of-the-art ab initio calculations were employed.
• Second-order Møller-Plesset perturbation theory (MP2) was utilized for high-accuracy energy calculations.
• Calculations covered a range of PAHs, including coronene, and Li+/Na+ cations.

Main Results:

• A substantial nonadditive contribution to H2 binding energy was observed.
• For Li+, the PAH significantly weakened H2 binding (~20%), contrary to stabilization.
• For Na+, the PAH exerted a usual stabilizing influence on H2 binding, though less than pairwise additive predictions.
• Induction effects were identified as the dominant component of nonadditivity in H2-cation-benzene complexes.

Conclusions:

• Nonadditive effects are critical for accurately describing H2 binding in these ternary complexes.
• The nature and magnitude of nonadditivity depend strongly on the specific alkali cation.
• These findings highlight the limitations of pairwise additive models for complex molecular interactions.