An approach was proposed for evaluating the average velocities of adsorbate molecules in one-dimensional nanopore, when quantum tunnelling between neighboring potential minima leads to non-zero velocity. The approach was used to calculate the hydrogen isotope molecule (H2, D2, T2) velocities in ultra-thin carbon single-wall nanotubes (3,3) and (6,0). It was shown that the isotope mass difference leads to large differences of the quantum tunnelling value and large differences in the average molecule velocities, especially inside the tube (6,0). It was shown that different tube chirality led to markedly different velocities of adsorbate molecules, even if the diameters of both nanotubes did not differ significantly.

Isotope Velocity Differentiation in Thin Carbon Nanotubes through Quantum Diffusion. Fedorov, A.S., Avramov, P.V., Ovchinnikov, S.G., Kresse, G.: Europhysics Letters, 2003, 63[2], 254-60