Reactions of ultracold alkali-metal dimers

We investigate the energetics of reactions involving pairs of alkali-metal dimers. Atom exchange reactions to form homonuclear dimers are energetically allowed for some but not all of the heteronuclear dimers. We carry out high-level electronic structure calculations on the potential energy surfaces of all the heteronuclear alkali-metal trimers and show that trimer formation reactions are always energetically forbidden for low-lying singlet states of the dimers. The results have important implications for the stability of quantum gases of alkali-metal dimers.

Figure 1

(Top) The intersecting potential energy surfaces for ${}^2{A}_1$ and ${}^2{B}_2$ states of Rb${}_2$Cs at $C_{2v}$ geometries, as a function of the RbCs bond length $r$ and the bond angle $\theta$. (Bottom) Curves for the ${}^2{A}_1$ and ${}^2{B}_2$ states of Rb${}_2$$X$ systems as a function of bond angle $\theta$, with the bond length optimized at each angle. For $X=\mathrm{Li}$, Cs, K the minima for ${}^2{B}_2$ states are the absolute minima, while for the Rb${}_2$Na system the absolute minimum originates from the distorted ${}^2{A}_1$ minimum geometry.