Fig. S1.

Committor $p_{\text{B}}$ for configurations with a largest bubble of volume v. The configurations are randomly selected points along reactive trajectories at a pressure of $-150\hspace{0.17em}\text{MPa}$. The yellow line is a fit using a hyperbolic tangent, error bars are $\pm \sigma$, and the dashed brown line indicates the location $v^{*}$ of the maximum in the free energy barrier shown in Fig. 1.