Global Full-Dimensional Potential Energy Surface for the Reaction 23 Na 87 Rb + 23 Na 87 Rb → 23 Na 2 + 87 Rb 2 and the Formation Rate and Lifetime of the 23 Na 2 87 Rb 2 Collision Complex.

A full-dimensional global potential energy surface (PES) for the reaction 23 Na 87 Rb + 23 Na 87 Rb → 23 Na 2 + 87 Rb 2 was constructed based on high-level ab initio calculations. The short-range part was expressed as a permutation invariant polynomial-neural network (PIP-NN) fit of 22 003 ab initio points calculated using a coupled cluster method with the one-electron basis 5 s 5 p 5 d 2 f plus effective core potentials and core polarizability potentials, while the long-range part was represented in an asymptotically correct form based on multipole expansion. The formation rate of the 23 Na 2 87 Rb 2 complex calculated using a quantum statistical method is in good agreement with experiment, while the estimated 19.20 μs lifetime of the complex from Rice-Ramsperger-Kassel-Marcus (RRKM) theory is significantly shorter than the measured millisecond decay rate, signaling either the inadequacy of RRKM theory or a yet unresolved loss mechanism.