Abstract
The geometric phase is shown to control the outcome of an ultracold chemical reaction. The control is a direct consequence of the sign change on the interference term between two scattering pathways (direct and looping), which contribute to the reactive collision process in the presence of a conical intersection (point of degeneracy between two Born–Oppenheimer electronic potential energy surfaces). The unique properties of the ultracold energy regime lead to an effective quantization of the scattering phase shift enabling maximum constructive or destructive interference between the two pathways. By taking the O+OH→H+O2 reaction as an illustrative example, it is shown that inclusion of the geometric phase modifies ultracold reaction rates by nearly two orders of magnitude. Interesting experimental control possibilities include the application of external electric and magnetic fields that might be used to exploit the geometric phase effect reported here and experimentally switch on or off the reactivity.
Highlights
The geometric phase is shown to control the outcome of an ultracold chemical reaction
The geometric phase (GP) effect in molecules refers to the sign change associated with the Born–Oppenheimer adiabatic electronic wave function when transported along a closed path encircling a conical intersection (CI), a point of degeneracy between two electronic potential energy surfaces (PESs)
Large GP effects are predicted to occur in ultracold chemical reactions, for which: (a) the relevant Born–Oppenheimer adiabatic electronic PES exhibits a CI, (b) the direct and looping contributions to the scattering amplitude are of similar magnitude and (c) their phases are quantized
Summary
The geometric phase is shown to control the outcome of an ultracold chemical reaction. Large GP effects are predicted to occur in ultracold chemical reactions, for which: (a) the relevant Born–Oppenheimer adiabatic electronic PES exhibits a CI, (b) the direct and looping contributions to the scattering amplitude are of similar magnitude and (c) their phases are quantized (or nearly so). These three conditions are readily met in the experimentally relevant O þ OH (v 1⁄4 0, j 1⁄4 0)-H þ O2 (v0, j0) reaction, which will serve as our prototypical system. Numerous experimental and theoretical studies of collisions involving OH molecules in the cold and ultracold temperature regimes have been reported in recent years, and the O þ OH reaction continues to be the topic of considerable experimental and theoretical investigations[33,34,35,36,37,38,39,40]
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