title: H + D2 Reaction Dynamics in the Limit of Low Product Recoil Energy.
abstract: Both experiment and theory recently showed that the H + D2(v = 0, j = 0) → HD(v' = 4, j') + D reactions at a collision energy of 1.97 eV display a seemingly anomalous HD product angular distribution that moves in the backward direction as the value of j' increases and the corresponding energy available for product recoil decreases. This behavior was attributed to the presence of a centrifugal barrier along the reaction path. Here, we show, using fully quantum mechanical calculations, that for low recoil energies, the collision mechanism is nearly independent of the HD internal state and the HD product becomes aligned, with its rotational angular momentum j' pointing perpendicular to the recoil momentum k'. As the kinetic energy to overcome this barrier becomes limited, the three atoms adopt a nearly collinear configuration in the transition-state region to permit reaction, which strongly polarizes the resulting HD product. These results are expected to be general for any chemical reaction in the low recoil energy limit.
authors: †Departamento de Química Física, Facultad de Química, Universidad de Salamanca, 37008 Salamanca, Spain.
authors: J
authors: J
authors: Aldegunde
authors: ‡Departamento de Química Física, Facultad de Química, Universidad Complutense, 28040 Madrid, Spain.
authors: D
authors: D
authors: Herráez-Aguilar
authors: ‡Departamento de Química Física, Facultad de Química, Universidad Complutense, 28040 Madrid, Spain.
authors: P G
authors: PG
authors: Jambrina
authors: ‡Departamento de Química Física, Facultad de Química, Universidad Complutense, 28040 Madrid, Spain.
authors: F J
authors: FJ
authors: Aoiz
authors: §Department of Chemistry, Stanford University, Stanford, California 94305-5080, United States.
authors: J
authors: J
authors: Jankunas
authors: §Department of Chemistry, Stanford University, Stanford, California 94305-5080, United States.
authors: R N
authors: RN
authors: Zare
keywords: alignment; reaction mechanism; stereodynamics