title: Quantum fluctuations increase the self-diffusive motion of para-hydrogen in narrow carbon nanotubes.
abstract: Quantum fluctuations significantly increase the self-diffusive motion of para-hydrogen adsorbed in narrow carbon nanotubes at 30 K comparing to its classical counterpart. Rigorous Feynman's path integral calculations reveal that self-diffusive motion of para-hydrogen in a narrow (6,6) carbon nanotube at 30 K and pore densities below ∼29 mmol cm(-3) is one order of magnitude faster than the classical counterpart. We find that the zero-point energy and tunneling significantly smoothed out the free energy landscape of para-hydrogen molecules adsorbed in a narrow (6,6) carbon nanotube. This promotes a delocalization of the confined para-hydrogen at 30 K (i.e., population of unclassical paths due to quantum effects). Contrary the self-diffusive motion of classical para-hydrogen molecules in a narrow (6,6) carbon nanotube at 30 K is very slow. This is because classical para-hydrogen molecules undergo highly correlated movement when their collision diameter approached the carbon nanotube size (i.e., anomalous diffusion in quasi-one dimensional pores). On the basis of current results we predict that narrow single-walled carbon nanotubes are promising nanoporous molecular sieves being able to separate para-hydrogen molecules from mixtures of classical particles at cryogenic temperatures.
authors.affiliation: Nanochemistry Research Institute, Department of Chemistry, Curtin University of Technology, P.O. Box U1987, Perth, 6845 Western Australia, Australia. Piotr.Kowalczyk@curtin.edu.au
authors.forename: Piotr
authors.initials: P
authors.lastname: Kowalczyk
authors.forename: Piotr A
authors.initials: PA
authors.lastname: Gauden
authors.forename: Artur P
authors.initials: AP
authors.lastname: Terzyk
authors.forename: Sylwester
authors.initials: S
authors.lastname: Furmaniak
mesh_terms: D006859:Hydrogen / Q000737:chemistry*; D056004:Molecular Dynamics Simulation; D037742:Nanotubes, Carbon / Q000737:chemistry*; D011789:Quantum Theory
chemical_list: D037742:Nanotubes, Carbon; D006859:Hydrogen