Dissociation of the fluorine molecule

Area of Science:

• Computational Chemistry
• Quantum Chemistry
• Thermochemistry

Background:

• Conflicting experimental and theoretical values exist for the dissociation energy of the fluorine molecule (D0(F2)) and the heat of formation of the fluorine atom (ΔfH0°(F)).
• Previous theoretical studies have disagreed on the presence of a barrier along the F2 dissociation curve.

Purpose of the Study:

• To resolve discrepancies in published thermochemical data for the fluorine molecule and atom.
• To provide accurate theoretical estimates for D0(F2) and ΔfH0°(F).
• To definitively determine the existence and characteristics of a barrier on the F2 dissociation curve.

Main Methods:

• High-accuracy coupled-cluster-based composite ab initio model chemistry was employed.
• Calculations included contributions up to pentuple excitations with basis set extrapolation.
• Extensive multireference configuration interaction and coupled-cluster calculations were performed to investigate the dissociation barrier.

Main Results:

• The study determined D0(F2) = 154.95 ± 0.48 kJ/mol and ΔfH0°(F) = 77.48 ± 0.24 kJ/mol.
• A dissociation barrier was confirmed to exist along the F2 curve at 3.80 ± 0.20 Å with a height of 42 ± 10 μEh.
• The confirmed barrier necessitates re-evaluation of experimental data that neglected this effect.

Conclusions:

• The theoretical estimates provide reliable thermochemical values for F2 and F.
• The existence of the dissociation barrier refines our understanding of F2 chemistry.
• The calculated values show excellent agreement with experimental results derived from ion-pair dissociation.