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Quantum control of molecular collisions at 1 kelvin

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Science  20 Oct 2017:
Vol. 358, Issue 6361, pp. 356-359
DOI: 10.1126/science.aao3116

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Tracking collisions in just one beam

Much of what we know about how quantum mechanics dictates chemical dynamics comes from half a century of studying controlled collisions between crossed pairs of molecular beams. Perreault et al. now show that even finer detail emerges in a study of hydrogen-deuterium (HD) collisions with D2 in a single beam. The experimental setup lowers the collision temperature to ∼1 K, allowing precise control over the rotational energy and relative alignment of the colliding partners. Scattering events in which HD loses rotational energy occurred three times as readily if the HD was aligned perpendicular rather than parallel to the beam-propagation axis.

Science, this issue p. 356

Abstract

Measurement of vector correlations in molecular scattering is an indispensable tool for mapping out interaction potentials. In a coexpanded supersonic beam, we have studied the rotationally inelastic process wherein deuterium hydride (HD) (v = 1, j = 2) collides with molecular deuterium (D2) to form HD (v = 1, j = 1), where v and j are the vibrational and rotational quantum numbers, respectively. HD (v = 1, j = 2) was prepared by Stark-induced adiabatic Raman passage, with its bond axis aligned preferentially parallel or perpendicular to the lab-fixed relative velocity. The coexpansion brought the collision temperature down to 1 kelvin, restricting scattering to s and p partial waves. Scattering angular distributions showed a dramatic stereodynamic preference (~3:1) for perpendicular versus parallel alignment. The four-vector correlation measured between the initial and final velocities and the initial and final rotational angular momentum vectors of HD provides insight into the strong anisotropic forces present in the collision process.

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