Energy Distribution Among Reaction Products. VI. F+H2, D2

Abstract

The infrared chemiluminescence (``arrested relaxation'') approach has been applied to the measurement of initial vibrational, rotational, and translational energies (V′, R′, and T′) in the products of the exothermic reactions F + H 2 → HF + H and F + D 2 → DF + D . Detailed rate constantsk(V′, R′, T′) are reported as contour plots. The total detailed rate constants into specified vibrational quantum states (summed over the rotational levels of each v′ level) are: (i) for F + H 2 , k(v′ = 1) = 0.31, [k(v′ = 2) = 1.00] , k(v′ = 3) = 0.47 ; (ii) for F+D2, k(v′ = 1) = 0.28, k(v′ = 2) = 0.65, [k(v′ = 3) = 1.00], k(v′ = 4) = 0.71 . Both reactions convert the total available energy quite efficiently into internal excitation of the new molecule. The mean fractions entering vibration plus rotation are: (i) for F+H2, f̄ V ′ + f̄ R ′ (= 0.66 ± 0.08) = 0.74; ( ii ) for F + D 2 , f̄ V ′ + f̄ R ′ ( = 0.66 + 0.08) = 0.74. The fractional conversion of available energy into vibration is comparable to that for the Cl+HI reaction (Part IV of this series) and markedly greater than that for H+Cl2 (Part V). It seems probable that the energy release is predominantly ``repulsive'' in all these reactions, but is more efficiently channeled into product vibration if the attacking atom is heavy (Cl+HI, F+H2). As in the case of other isotopic pairs of reactions (Parts IV and V of this series) there is a parallelism in k(V′) though not in k(v′) between the members of the pair. The present reactions exhibit only a small increase in product rotational excitation with decreasing vibrational excitation (— Δ R̂′ / Δ V′ more closely resembles that for the H+Cl2reaction than that for the reaction Cl+HI). It follows that the translational energy of the products is markedly greater for successively lower v′ states.