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21. May 2019 16:30

The interplay between short-range and long-range interactions in cold samples containing charges

Professor Robin Côté
Physics Department, University of Connecticut, Storrs, USA

In recent years, several studies of cold and ultracold hybrid systems involving atomic and molecular ions interacting with neutral atoms or molecules have led to rapid progress towards reaching the quantum regime, where a few partial waves contribute to the behavior of the system. In this work, we explore the effect of long-range interactions on the inelastic processes taking place at ultracold temperatures. We study how these long-range interactions couple to the shorter-range potential energy surfaces (PES) and can be used to explain /control the outcome of scattering events at low energy. In particular, we explore how the state of the projectile can influence the type of long-range interaction, leading to barriers that reduce or even prevent reactions in some cases, or accentuate the attractive polarization interaction that increase reaction rates in other cases. We present results on two polyatomic molecular ions reacting with excited Ca atoms, namely BaOCH3+  and BaCl+. For reactions to take place, Ca needs to be in an excited state, and the reaction rate depends strongly on the spin state of the excited state of Ca, i.e. either 1P or 3P.

We also discuss a different approach to affect charge exchange in atom-ion collision, namely using Feshbach resonance. This is a different example of using spin-states to affect reactions.

Finally, we present a simple formulation for the charge exchange in the case of resonant processes, linking the s-wave regime to higher temperatures. The expression is valid for resonant scattering processes in general (charge transfer, spin-flip, excitation exchange) under appropriate conditions, and could be used for quasi-resonant processes as well.

Partially supported by the MURI US Army Research Office Grant No. W911NF-14-1-0378.