Isotopic separation in mixed clusters of molecular hydrogen

We investigate mixed (50/50) clusters of parahydrogen and orthodeuterium at low temperatures, by means of quantum Monte Carlo simulations. Our results provide evidence of liquid-like behavior and partial isotopic separation in a cluster of 640 molecules, at temperature T = 10 K. As the temperature is lowered below ∼6 K, crystallization occurs, with no indication that the liquid phase is more resilient at low temperatures in a mixed cluster. Isotopic separation is therefore predicted to take place at low temperatures only through the slow process of molecular self-diffusion in a crystalline matrix.