A quasiclassical trajectory study of the time-delayed forward scattering in the hydrogen exchange reaction

Abstract

The time-delayed forward scattering mechanism recently identified by Althorpe et al. [Nature (London) 416, 67 (2002)] for the H+D2(v=0,j=0)→HD(v′=3,j′=0)+D reaction was analyzed by using quasiclassical trajectory (QCT) methodology. The QCT results were found to match the quantum wavepacket snapshots of Althorpe et al., albeit without the quantum scattering effects. Trajectories were analyzed on the fly to investigate the dynamics of the atoms during the reaction. The dominant reaction mechanism progresses from hard collinear impacts, leading to direct recoil, toward glancing impacts. The increased time required for forward scattered trajectories is due to the rotation of the transient HDD complex. Forward scattered trajectories display symmetric stretch vibrations of the transient HDD complex, a signature of the presence of a resonance, or a quantum bottleneck state.

Vibrationally inelastic collisions of H+D2: A comparison of quantum mechanical, quasiclassical, and experimental results

“…The collision times were determined by inspecting the evolution of the total relative energy as a function of time for each trajectory. The results are practically identical to those obtained with the method proposed by Greaves et al 10,11 The time independent QM calculations were carried out using the ABC code of Skouteris et al 12 At E coll = 1.72 eV, well converged DCSs were obtained using the following parameters: j max = 22, E max = 2.85 eV, k max = 10, J max = 48, max =25a 0 , and 250 sectors. Calculations carried out with k max = min͓J , jЈ͔ and with k max = 10 were indistinguishable.…”

Quantum interference between H + D2 quasiclassical reaction mechanisms

“…3b, namely small impact parameters and attacking angles far from collinearity. This mechanism, for which the transition state tends to be T-shaped, only takes place at a sufficiently high collision energy and has been discussed previously by Greaves et al 21,22 and termed 'the Ear'. This mechanism accounts for most of the reactivity at this collision energy and final states.…”

New, unexpected, and dominant mechanisms in the hydrogen exchange reaction

“…Similar trajectories were found in the HD͑Ј =3, jЈ͒ products of the title reaction and will be discussed in an adjacent paper. 26 These trajectories correspond to the well-known forward-scattered time-delayed mechanism, which was first conclusively identified by a combination of quantum wavepacket calculations and experimental measurements. 23 Later work 25 showed that the mechanism was caused by a superposition of "quantum bottleneck states," which cause the system to linger for about 10-25 fs on top of the effective adiabatic-reaction barriers.…”

“…[23][24][25] We have examined the short-lived collision complex invoked to explain this forward scattering in an adjacent paper. 26 Standard plots of PESs highlight the MEP as they use internal coordinates, e.g., two distances at fixed bending angle ͑linear͒ showing the reactant and product channels. We find it more instructive to plot the H 3 potential at fixed diatom distance as a function of position of the third atom ͑see Fig.…”