Non-universal Quantum Dynamics of Ultracold Chemical Reactions of Polar Alkali-dimer Molecules with Alkali-metal Atoms: Li($^2$S) +NaLi($a^3\Sigma^+$) $\to$ Na($^2$S) + Li$_2$($a^3\Sigma_u^+$)

Ultracold chemical reactions of weakly bound triplet-state alkali-metal dimer molecules have recently attracted much experimental interest. We use rigorous quantum scattering calculations based on a newly constructed accurate ab initio potential energy surface to explore the chemical reaction of spin-polarized NaLi( a 3 Σ + ) molecules and Li( 2 S) atoms to form Li 2 ( a 3 Σ + u ) and Na( 2 S), a candidate for non-universal dynamics. The reaction is exothermic, and proceeds readily at ultralow temperatures with the ratio of elastic to reactive collision rate coefficients γ < 0 . 011 at 1 µ K. Significantly, we observe strong sensitivity of the total reaction rate to small variations of the three-body part of the Li 2 Na interaction at short range, a signature of highly non-universal reaction dynamics. The breakdown of universality occurs despite the deep and barrierless potential energy surface. We attribute this to a relatively small number of open Li 2 ( a 3 Σ + u ) product channels that are populated in the reaction as compared to the chemical reactions of covalently bound ground-state alkali dimers studied before. The present result provides the first signature of highly non-universal dynamics seen in rigorous quantum reactive scattering calculations on an