Bifurcation of Reaction Complex Lifetimes in Ultracold Rb + KRb Reactions

Chemical reactions, with typical eV-scale energies, are usually considered chaotic, statistical processes. Deviations from such behavior hold the potential for coherent dynamics, opening new avenues in quantum chemistry. Past measurements of the Rb + KRb reaction in the ultracold regime [1] showed the reaction complex lifetime exceeding the statistical RRKM prediction by five orders of magnitude.

A proposed mechanism suggests the existence of states trapped in the complex due to destructive interference in the exit channel, hinting toward lifetimes shorter than the statistical prediction. We identify such short-lived states by observing the reaction products and measuring the optical intensity required to suppress them via photo-excitation of the complex.

To further probe the complex dynamics, we implement nuclear-spin-sensitive detection of the products and find that atom-exchange processes lead to nuclear spin flips during the reaction. Our results provide insight into the mechanisms underlying the observed bifurcation between short- and long-lived complexes and shed light on the exceptionally long lifetime puzzle.

[1] Nichols, M.A., Liu, Y.X., Zhu, L., Hu, M.G., Liu, Y. and Ni, K.K., 2022. Detection of long-lived complexes in ultracold atom-molecule collisions. Physical Review X, 12(1), p.011049.