The problematic C2H4+F2 reaction barrier.

Area of Science:

• Physical Chemistry
• Computational Chemistry
• Chemical Kinetics

Background:

• The reaction between ethylene (C2H4) and fluorine (F2) is a fundamental process in combustion and atmospheric chemistry.
• Accurate theoretical data is crucial for understanding reaction mechanisms and predicting outcomes.
• Previous experimental studies have reported varying activation energies for this reaction.

Purpose of the Study:

• To investigate the C(2)H(4)+F(2) reaction using high-level ab initio electronic structure methods.
• To accurately determine the reaction barrier and enthalpy of formation for the fluoroethyl radical.
• To provide a theoretical benchmark for comparison with experimental data.

Main Methods:

• Employed a focal point approach to achieve convergence towards the ab initio limit.
• Utilized large basis sets (up to aug-cc-pV5Z) and extensive correlation treatments (CCSDT(Q)).
• Included auxiliary core correlation, diagonal Born-Oppenheimer, and relativistic corrections.

Main Results:

• Calculated a theoretical reaction barrier of 8.0 kcal mol(-1) for C(2)H(4)+F(2).
• This theoretical barrier is significantly higher than the recent experimental value of 5.5+/-0.5 kcal mol(-1).
• Determined a new enthalpy of formation for the fluoroethyl radical (ΔfH°(C2H4F)) as -13.2+/-0.2 kcal mol(-1), with improved accuracy.

Conclusions:

• The rigorous theoretical investigation suggests a higher activation energy for the C(2)H(4)+F(2) reaction than previously reported experimentally.
• The calculated enthalpy of formation for the fluoroethyl radical offers a more precise value compared to prior experimental determinations.
• Discrepancies between theory and experiment warrant further investigation into the reaction dynamics and potential experimental error sources.