Energy Distribution Among Reaction Products. IV. X+HY (X ≡ Cl, Br; Y ≡ Br, I), Cl+DI

Abstract

The distribution of vibrational, rotational, and translational energies (symbolized by V′, R′, and T′) have been obtained for the products of the isotopic pair of reactions Cl + HI → HCl + I and Cl + DI → DCl + I. The experimental method was the ``arrested relaxation'' variant of the infrared chemiluminescence technique. Detailed rate constants k(V′, R′, T′) are reported in the form of contour plots for these reactions. The total detailed rate constants into specified vibrational quantum states for Cl+HI (summed over the rotational levels of each v′ level) are k(v′ = 1) = 0.22, k(v′ = 2) = 0.35, [k(v′ = 3) = 1.00], k(v′ = 4) = 0.74; and for Cl + DI, k(v′ = 1) ≈ 0.08, k(v′ = 2) = 0.14, k(v′ = 3) = 0.35, k(v′ = 4) = 0.73, [k(v′ = 5) = 1.00], k(v′ = 6) = 0.05 [relative to the highest rate constant k(v̂′) = 1.00, in each case]. Preliminary energy distributions are also reported for the products of two other reactions, Cl + HBr → HCl + Br and Br + HI → HBr + I, in the X + HY → HX + Y family (X and Y are halogen atoms). The members of this family of reactions channel a substantial fraction of the energy available to the products into vibrational and rotational excitation, and only a small fraction into relative translation. For the Cl+HI and also the Cl+DI reaction the fractions are f̄V′ + f̄R′ (= 0.71 + 0.13) = 0.84; in contrast to f̄T′ = 0.16. As a corollary there is a marked inverse correlation between vibrational and rotational excitation in the reaction products. Despite the fact that the detailed rate constants into specified product quantum states [k(v′, J′)] are markedly different for the isotopic pair of reactions, the fractional conversion of the available energy into vibration, rotation, and translation are in close agreement (to ∼ ± 1%). This close parallelism in f̄V′, f̄R′, f̄T′ is in accord with predictions from classical trajectory studies. It indicates the usefulness of such calculations even for the case of reactions which yield products with widely spaced (vibrational and rotational) quantum levels.