Due to the large size of the considered systems, we were forced to use a more internallycontracted version 37 of CASPT2 for the potential evaluations for R2 -R4. Since geometry relaxation effects were not expected to change significantly and the explicitly-correlated methods with large basis sets were computationally infeasible for these systems, we chose to apply the correction potential obtained for 2 CF 3 --→ ←--C 2 F 6 to all the reactions considered.