Formation of the HHF complex in the reaction of thermal fluorine atoms with hydrogen molecules in solid Ar

The reaction of F atoms with H2 in an Ar matrix was studied with EPR spectroscopy. F2 photolysis produces two well-known doublets of the H atom trapped in different crystal sites. Heating gives rise to an EPR spectrum assigned to the H2F complex (AH = 50.8, AF = 1.85, AH ⩽ 0.15 mT), the formation of which is attributed to the reaction of diffusing thermal Ft atoms with H2. The shape and width of the spectrum of the complex changes drastically with temperature due to the transitions between two stable configurations: A (aF = 3.2 mT, aH ⩽ 3.2 mT) and B (aF = 0.5 mT, aH = 0.4 mT) with an Arrhenius-like dependence of rate (Ea = 80 cal/mol, ω0 ∼ 3 × 1010 s−1).