Accurate Theoretical Thermochemistry for Fluoroethyl Radicals

Area of Science:

• Computational Chemistry
• Thermochemistry
• Fluorinated Hydrocarbons

Background:

• Hydrofluorocarbons (HFCs) are crucial in various industrial applications.
• Accurate thermochemical data for HFC radicals is essential for understanding reaction mechanisms and kinetics.
• Existing data for many HFC radicals may lack the required precision for detailed modeling.

Purpose of the Study:

• To compute highly accurate thermochemical quantities, specifically heats of formation and entropy data, for a series of hydrofluorocarbon radicals.
• To establish a reliable computational model chemistry for predicting these properties with high precision.
• To resolve discrepancies between theoretical and experimental thermochemical data.

Main Methods:

• Application of an accurate coupled-cluster (CC) based model chemistry.
• Inclusion of iterative triple and perturbative quadruple excitations in CC theory.
• Incorporation of scalar relativistic and diagonal Born-Oppenheimer corrections.

Main Results:

• Reliable thermochemical quantities, including heats of formation and entropy, were calculated for eight hydrofluorocarbon radicals.
• Perturbative quadruple excitations and scalar relativistic corrections were found to be essential for achieving better than chemical accuracy.
• The contribution of these corrections to heats of formation increases with fluorine content, reaching 10 kJ/mol for pentafluoroethyl radical.

Conclusions:

• The study delivers the most accurate heat of formation and entropy data currently available for the investigated radicals.
• The developed model chemistry provides a robust tool for future thermochemical calculations of fluorinated compounds.
• Discrepancies with experimental data were resolved by recalculating with updated auxiliary data, validating the computational approach.