The problematic C_2H_4+F_2 reaction barrier

摘要

The C_2H_4+F_2 reaction is investigated through the most rigorous electronic structure methods currently feasible, using a focal point approach to converge toward the ab initio limit. Explicit computations were executed with basis sets as large as aug-cc-pV5Z and correlation treatments as extensive as coupled cluster through full triples with a perturbative inclusion of quadruple excitations CCSDT(Q). Auxiliary core correlation, diagonal Born–Oppenheimer, and first-orderrelativistic corrections were included. All optimized geometries and vibrational frequencies were determined completely at the CCSD(T)/aug-cc-pVQZ level. The final C_2H_4+F_2 reaction barrier from theory (8.0 kcal mol~(-1) is significantly higher than the recently reported experimental barrier (5.5±0.5 kcal mol~(-1). Our computations also yield a new enthalpy of formation of the fluoroethyl radical, △_fH_298~° (C_2H_4F)=-13.2±0.2 kcal mol~(-1), whose uncertainty is an order of magnitude less than previous experimental values.