Chemical reactions of ultracold alkali-metal dimers in the lowest-energy $^3\Sigma$ state

TL;DR

This paper investigates the chemical reactivity of ultracold alkali-metal dimers in the $^3\Sigma$ state, revealing barrierless reactions and the necessity of optical lattices to prevent molecular loss.

Contribution

It provides the first detailed analysis of reaction pathways and energy barriers for ultracold alkali dimers, highlighting their inherent chemical instability.

Findings

Reactions are barrierless and lead to homonuclear dimers or trimers.

All alkali dimers in the $a^3\Sigma^+$ state are chemically unstable at ultracold temperatures.

Reaction of alkali hydrides is accelerated, producing energetic hydrogen atoms.

Abstract

We show that the interaction of polar alkali dimers in the quintet spin state leads to the formation of a deeply bound reaction complex. The reaction complex can decompose adiabatically into homonuclear alkali dimers (for all molecules except KRb) and into alkali trimers (for all molecules). We show that there are no barriers for these chemical reactions. This means that all alkali dimers in the $a^3\Sigma^+$ state are chemically unstable at ultracold temperature, and the use of an optical lattice to segregate the molecules and suppress losses may be necessary. In addition, we calculate the minimum energy path for the chemical reactions of alkali hydrides. We find that the reaction of two molecules is accelerated by a strong attraction between the alkali atoms, leading to a barrierless process that produces hydrogen atoms with large kinetic energy. We discuss the unique features of the chemical reactions of ultracold alkali dimers in the $a^3\Sigma^+$ electronic state.