Quantum interference between H + D2 quasiclassical reaction mechanisms

Abstract

Interferences are genuine quantum phenomena that appear whenever two seemingly distinct classical trajectories lead to the same outcome. They are common in elastic scattering but are seldom observable in chemical reactions. Here we report experimental measurements of the state-to-state angular distribution for the H + D2 reaction using the 'photoloc' technique. For products in low rotational and vibrational states, a characteristic oscillation pattern governs backward scattering. The comparison between the experiments, rigorous quantum calculations and classical trajectories on an accurate potential energy surface allows us to trace the origin of that structure to the quantum interference between different quasiclassical mechanisms, a phenomenon analogous to that observed in the double-slit experiment.

Dynamical importance of van der Waals saddle and excited potential surface in C(1D)+D2 complex-forming reaction

“…4b, which exhibits an interesting oscillation pattern with peaks. This phenomenon may be caused by quantum interferences between partial waves, which appears to be similar to the diffraction oscillations just observed experimentally in the H+D 2 reaction by Zare and coworkers using the photoloc technique4041. However, they are of different nature, and as demonstrated by Zare and coworkers41, the latter is caused by well separated sets of total angular momentum, leading to scattering at the same angles.…”

Effects of reagent rotation on interferences in the product angular distributions of chemical reactions

“…10 Specifically, for initial j = 0, the interference pattern was observed whenever two separated groups of J gave rise to scattering at the same angles. We could therefore expect that the smoothed interference pattern would be associated with a significant change in its QCT deflection function.…”

“…1) with increasing j ′ can be traced back to differences in the quasiclassical D r ( J , θ ). 10 Whereas for j ′ = 0 there is a neat separation between the main two mechanisms, they merge at high j ′, 10 causing the interferences to vanish. Following the double-slit analogy, the two slits merge where j ′ is sufficiently high.…”

“…In a recent article, 10 we measured state-to-state angular distributions of the HD product reactively scattered at a collision energy, E coll , of 1.97 eV, for the benchmark H + D 2 → D + HD reaction using the photoloc technique. 11,12 The angular distribution, or differential cross section (DCS), represents the cross section as a function of the scattering angle, θ , and its QM value is obtained as the square of a coherent sum of partial waves from the different values of the total angular momentum, J .…”

“…10 These results could not be accounted for by the QCT method, wherein the nuclei are treated as classical particles moving on a potential energy surface (PES) originating from quantum electronic motions, even though it usually constitutes a very good approximation for the dynamical description of the H + D 2 and many other chemical reactions. 14 The fact that the measurements could only be reproduced by exact QM calculations (where both nuclei and electrons are treated quantum mechanically) clearly indicated that the observed oscillatory pattern in the angular distribution was caused by a quantum phenomenon.…”