AMO
In the literature: open
First-principles lifetime of the four-atom collision complex
In plain words
When two molecules stick, the lifetime of the pair depends on how many internal states it can explore. Calculations of this count disagree with some measurements.
Precise statement
For $(\mathrm{NaK})_2$, $(\mathrm{RbCs})_2$ and $\mathrm{KRb} + \mathrm{KRb}$, compute the sticking lifetime $\tau = 2 \pi \hbar \rho / N_o$, with $\rho$ the density of states of the complex at threshold including conserved total angular momentum, parity and nuclear spin, and $N_o$ the number of open channels. Answer: $\tau$ for each system within a factor 2 of measured values, or a quantified failure of statistical theory.
What would settle it
Ab initio density-of-states calculations compared with direct complex-lifetime measurements in light-free traps.