Quantum adsorbates: Path integral Monte Carlo simulations of helium in silicalite

Quantum effects on He-3 and He-4 sorption in silicalite were studied using Fourier path integral Monte Carlo simulations. A helium-silicalite interaction potential was constructed on the basis of the Kiselov model. Simulations were performed over a temperature range 7.5-50 K in the dilute limit when interparticle interactions are negligible. Quantum delocalization was shown to reduce isosteric heats of sorption by up to 25% and specific heats by up to 60% in this temperature range. The difference between the isosteric heats of sorption of He-3 and He-4 was found to be less that 3% at the temperatures studied. The quantum and classical potential energy distributions were monitored as a function of temperature and were shown to be substantially different below 20 K. The strong potential exerted by the zeolite lattice was shown to appreciably reduce the extent of quantum fluctuations.