Relative efficacy of vibrational vs. translational excitation in promoting atom-diatom reactivity: Rigorous examination of Polanyi's rules and proposition of sudden vector projection (SVP) model

Abstract

To provide a systematic and rigorous re-examination of the well-known Polanyi's rules, excitation functions of several A + BC(v = 0, 1) reactions are determined using the Chebyshev real wave packet method on accurate potential energy surfaces. Reactions with early (F + H2 and F + HCl), late (Cl + H2), and central (H∕D∕Mu + H2, where Mu is a short-lived light isotope of H) barriers are represented. Although Polanyi's rules are in general consistent with the quantum dynamical results, their predictions are strictly valid only in certain energy ranges divided by a cross-over point. In particular, vibrational excitation of the diatomic reactant typically enhances reactivity more effectively than translational excitation at high energies, while reverse is true at low energies. This feature persists irrespective of the barrier location. A sudden vector projection model is proposed as an alternative to Polanyi's rules. It is found to give similar, but more quantitative, predictions about mode selectivity in these reactions, and has the advantage to be extendible to reactions involving polyatomic molecules.

On the origin of mode- and bond-selectivity in vibrationally mediated reactions on surfaces

“…63 Jiang, Guo and co-workers report that a sudden vector projection model, which assumes no IVR during the reactive encounter, successfully captures the dominant dynamical features of methane activation. 47,64,65 In all of these cases, surface-induced IVR will be restricted to initial energy redistribution into a small number of strongly coupled doorway states. The timescale for surface approach in hyperthermal beam-surface scattering is accelerated relative to the situation illustrated in Fig.…”

Bond-Selective and Mode-Specific Dissociation of CH3D and CH2D2 on Pt(111)

“…Alternatively, the so-called sudden vector projection model (SVP) was recently proposed by some of the current authors 20,21 to explain and predict vibrational mode specificity and bond selectivity both in bimolecular gas-phase and in gas− surface reactions. The SVP model assumes that IVR within the reactants is much slower than the time scale of the reactive collision and therefore treats the reaction as sudden; i.e., it neglects the surface-induced IVR processes that are calculated in Jackson's RPH model.…”

State-to-state quantum dynamics of the F + HCl (vi = 0, ji = 0) → HF(vf, jf) + Cl reaction on the ground state potential energy surface

“…The energy disposal can be further understood in terms of the newly proposed sudden vector projection (SVP) model. 48 In the lower panel of Fig. 3, we compare, at a collision energy of 4.3 kcal mol À1 , the experimentally determined 18 vibrational state distribution of the HF products, summed over rotational levels, with the predictions of the present calculations along with those of the previous QM and QCT studies.…”