A Monte Carlo simulation of a thirteen-atom argon cluster in supercage
s of zeolite NaCaA is reported. The confined cluster undergoes distort
ion giving a peak in the angle distribution function at around 90 degr
ees. The structure, energetics and other properties are dictated by a
competition between guest-guest and guest-zeolite interactions. It is
found that the cluster melts in the region from 25 to 40 K. The change
in delta during melting is smaller than that observed for bulk matter
or that for the free cluster, which we attribute to confinement.