Anomalous Lifetimes of Ultracold Complexes Decaying into a Single Channel: What's Taking So Long in There?

TL;DR

This paper explores why ultracold molecular complexes with a single decay channel have unexpectedly long and nonexponential lifetimes, using theoretical models to match experimental observations.

Contribution

It introduces a theoretical framework combining transition-state theory and an optical model to explain anomalously slow decay rates in ultracold complexes with one open channel.

Findings

Complexes with a single open channel can have very slow decay rates.

Decay processes can be nonexponential in time.

The theory qualitatively matches experimental data for RbCs and NaRb.

Abstract

We investigate the lifetimes of complexes formed in ultracold molecule collisions. Employing both transition-state-theory and an optical model approach we examine processes that can extend the lifetime of complexes beyond that predicted by Rice-Ramsperger-Kassel-Marcus theory. We focus on complexes that possess only one open channel, and find that the extreme distribution of widths for this case favors low decay rates. Thus decay from a complex into a single energetically available channel can be anomalously slow, and moreover nonexponential in time. We apply the theory to two systems of current experimental interest, RbCs and NaRb, finding qualitatively that the empirical time scales can be accounted for in the theory.