Combination of CF(3)CHF and CF(3) radicals at room temperature generated chemically activated CF(3)CHFCF(3) molecules with 95 +/- 3 kcal/mol of internal energy that decompose by loss of HF, initially attached to adjacent carbons, with an experimental unimolecular rate constant of (4.5 +/- 1.1) x 10(2) s(-1). Density functional theory was used to model the unimolecular rate constant for HF elimination, k(HF), to determine a threshold energy of 75 +/- 2 kcal/mol.