Chemical pathways in ultracold reactions of SrF molecules

We present a theoretical investigation of the chemical reaction SrF + SrF -> products, focusing on reactions at ultralow temperatures. We find that bond swapping SrF + SrF -> Sr-2 + F-2 is energetically forbidden at these temperatures. Rather, the only energetically allowed reaction is SrF + SrF -> SrF2 + Sr, and even then only singlet states of the SrF2 trimer can form. A calculation along a reduced reaction path demonstrates that this abstraction reaction is barrierless and proceeds by one SrF molecule "handing off" a fluorine atom to the other molecule.