  Continuum Monte-Carlo simulations at constant pressure are performed on short
chain molecules at surfaces. The rodlike chains, consisting of seven effective
monomers, are attached at one end to a flat twodimensional substrate. It is
found that the model exhibits phases similar to the liquid condensed and liquid
expanded phases of Langmuir monolayers. The model is investigated here for a
wide range of pressures and temperatures using a special form of constant
pressure simulation compatible with the symmetry breaking during tilting
transitions in the liquid condensed phases. At low pressures the chains undergo
a tilting transition exhibiting tilt directions towards nearest and also next
nearest neighbours depending on temperature. At elevated temperatures and low
pressure the film enters a fluidlike phase similar to whose surface area per
molecule is in rough quantitative agreement with that of the liquid expanded
phase observed in experiment.
