Differential cross section for the H+D2→HD(v′=1,j′=2,6,10)+D reaction as a function of collision energy

Abstract

We have measured differential cross sections (DCSs) for the HD (v(')=1,j(')=2,6,10) products of the H+D(2) exchange reaction at five different collision energies in the range 1.48< or =E(coll)< or =1.94 eV. The contribution from the less energetic H atoms formed upon spin-orbit excitation of Br in the photolysis of the HBr precursor is taken into account for two collision energies, E(coll)=1.84 and 1.94 eV, allowing us to disentangle the two different channels. The measured DCSs agree well with new time-dependent quantum-mechanical calculations. As the product rotational excitation increases, the DCSs shift from backward to sideward scattering, as expected. We also find that the shapes of the DCSs show only a small overall dependence on the collision energy, with a notable exception occurring for HD (v(')=1,j(')=2), which appears bimodal at high collision energies. We suggest that this feature results from both direct recoil and indirect scattering from the conical intersection.

Simultaneous Measurement of Reactive and Inelastic Scattering: Differential Cross Section of the H + HD → HD(v′, j′) + H Reaction

“…Calculations by Kuppermann and co-workers in the early 90s predicted significant differences in experimental observables between calculations ignoring and including the GP effect [47,48]. Experimental measurements however were a very good fit to theory that did not take the GP into account [2,[7][8][9]12,49]. Following earlier work by Kendrick [50], Althorpe and co-workers [33,37,38,51,52] succeeded in proving definitively that the GP has no effect on the ICS and only a minor effect on the DCS at E coll < ∼ 4 eV.…”

“…Actual recoil values are tabulated in Table 1. In our earlier studies this inherent uncertainty in the speed of HD(ν , j ) product was taken into account by convoluting the theoretical calculations with a ∼ 200 m/s wide Gaussian, i.e., typical HD + recoil values, see Table 1 [7][8][9]. Here we add the appropriate error bars on experimentally measured points rather than further blurring theoretical calculations.…”

“…Indeed, similar conclusions were reached by Fernandez-Alonso et al [40] who measured the D 2 (v = 0, j) reactant rotational state distribution and found that about 10% of the population resides in D 2 (v = 0, j > 2) states. Subsequently, all theoretical calculations on H + D 2 reaction were performed assuming only three initial reactant states, i.e., D 2 (v = 0, j ≤ 2), and the agreement in most cases was found to be very good [7][8][9]. The last source of uncertainty in the experimental measurement of HD(ν , j ) laboratory speed is the HD + recoil imparted by the departing electron.…”

“…Indeed, this is part of the reason why the reactive scattering of the H + D 2 and D + H 2 reactions has received considerably more experimental attention than the inelastic process. It is well known that reactive encounters between a hydrogen atom and a hydrogen molecule are mostly direct in nature [1][2][3][4][5][6][7][8]. According to this model, small-impactparameter collisions lead to rotationally cold, backward scattered products, while glancing, large-impact-parameter collisions produce rotationally excited, sideways/forward scattered products.…”

Benchmarking Quantum Chemical Methods: Are We Heading in the Right Direction?

“…It is worth mentioning the counterpart to the H 2 energy challenge in reaction dynamics and kinetics: the H+H 2 reaction. Ever since the archetypical representation of its reaction surface73 it has been the subject of countless detailed experimental benchmarking efforts 74. Scattering experiments and time‐resolved spectroscopy continue to provide the most valuable reference data for chemical dynamics and thus the time‐dependent Schrödinger equation.…”