Isotopic separation in mixed clusters of molecular hydrogen

TL;DR

This study uses Quantum Monte Carlo simulations to explore isotopic separation and phase behavior in mixed hydrogen-deuterium clusters at low temperatures, revealing liquid-like states, crystallization, and slow isotopic diffusion.

Contribution

It provides the first detailed simulation-based evidence of isotopic separation and phase transitions in mixed hydrogen clusters at low temperatures.

Findings

Liquid-like behavior and partial isotopic separation at 10 K

Crystallization occurs below approximately 6 K

Isotopic separation involves slow molecular self-diffusion in crystals

Abstract

We investigate mixed (50/50) clusters of parahydrogen and orthodeuterium at low temperature, 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 temperature in a mixed cluster. Isotopic separation is therefore predicted to take place at low temperature only through the slow process of molecular self-diffusion in a crystalline matrix.