Reactions of H(2), HD, and D(2) with H(2)(+), HD(+), and D(2)(+): Product-Channel Branching Ratios and Simple Models

[Image: see text] We present measurements of the product-channel branching ratios of the reactions (i) HD(+) + HD forming H(2)D(+) + D (38.1(30)%) and HD(2)(+) + H (61.9(30)%), (ii) HD(+) + D(2) forming HD(2)(+) + D (61.4(35)%) and D(3)(+) + H (38.6(35)%), and (iii) D(2)(+) + HD forming HD(2)(+)+ D (60.5(20)%) and D(3)(+) + H (39.5(20)%) at collision energies E(coll) near zero, i.e., below k(B) × 1 K. These branching ratios are compared with branching ratios predicted using three simple models: a combinatorial model (M1), a model (M2) describing the reactions as H-, H(+)-, D-, and D(+)-transfer processes, and a statistical model (M3) that relates the reaction rate coefficients to the translational and rovibrational state densities of the H(n)D(3–n)(+) + H/D (n = 0, 1, 2 or 3) product channels. The experimental data are incompatible with the predictions of models M1 and M2 and reveal that the branching ratios exhibit clear correlations with the product state densities.