  Adsorption properties of several gases (Ne, CH4, Ar, Xe) on the external
surface of a carbon nanotube bundle are investigated. Calculations are
performed at low coverage and variable temperature, and for some temperatures
as a function of coverage. Within a simple model (in the limit of very low
coverage) we are able to study the evolution of the film's thermal properties
from those of a one dimensional (1D) fluid to those of a 2D film. In addition,
grand canonical Monte Carlo simulations are performed in order to identify a
second layer groove phase, which occurs once a monolayer of atoms covers the
external surface. We derive from the simulations the isosteric heat,
compresibility and specific heat as a function of coverage. We evaluate
alternative models in order to derive quantum corrections to the classical
results. We compare our findings with those of recent adsorption experiments.
