Simulations show that ${\mathrm{CO}}_2$ adsorbed in the groove sites of carbon nanotubes displays unique quasi-one-dimensional behavior. Clusters containing only odd numbers of molecules are formed at finite ${\mathrm{CO}}_2$ coverages and low temperatures. The molecules are orientationally ordered with respect to the nanotube groove axis and azimuthally ordered in the plane perpendicular to the groove axis. This ordering is a result of a delicate balance between solid-fluid and fluid-fluid forces; the ${\mathrm{CO}}_2$ quadrupole plays a critical role in the cluster formation and orientational ordering.

• Received 22 July 2004

DOI:https://doi.org/10.1103/PhysRevLett.94.125701