Eur. Phys. J. B 48, 113-124 (2005)
https://doi.org/10.1140/epjb/e2005-00378-9

Nanotube field and one-dimensional fluctuations of C₆₀ molecules in carbon nanotubes

¹ Department of Physics, University of Antwerp, Groenenborgerlaan 171, 2020 Antwerpen, Belgium
² Institute of Physical Chemistry of the Russian Academy of Sciences, Leninskii prospekt 31, 117915, Moscow, Russia

Corresponding author: ^a bart.verberck@ua.ac.be

Received: 24 June 2005
Revised: 21 September 2005
Published online: 9 December 2005

Abstract

C molecules encapsulated in carbon nanotubes interact by van der Waals forces with the tube walls. The nanotube field leads to orientational confinement of the C molecules which depends on the nanotube radius. In small tubes with radius  Å a fivefold symmetry axis of the molecule coincides with the tube axis, the center of mass of the molecule being located on the tube axis. The interaction between C molecules encapsulated in the nanotube is then described by a O₂-rotor model on a one-dimensional (1-d) liquid chain with coupling between orientational and displacive degrees of freedom but no long-range order. This coupling leads to a temperature-dependent chain contraction. The structure factor of the 1-d liquid is derived. In tubes with larger radius the molecular centers of mass are displaced off the tube axis. The distinction of two groups of peapods with on- and off-axis molecules suggests an explanation of the apparent splitting of A_g modes of C in nanotubes measured by resonant Raman scattering.