A recently suggested computational scheme lsqb;Buch and Devlin, J. Chem. Phys.98, 4195 (1993)rsqb; is extended to describe orientational phenomena in systems containing assemblies of oddhyphen;Jand evenhyphen;Jhydrogen and deuterium molecules. Nuclear symmetry and rotational effects are incorporated in the path integral Monte Carlo algorithm. The scheme is employed in a study of the (parahyphen;D2)3(orthohyphen;D2)10and (parahyphen;D2)13clusters in the 1ndash;3 K temperature range. In the (parahyphen;D2)3(orthohyphen;D2)10cluster at 1 K, the threeJ=1 molecules form a lsquo;lsquo;cluster within cluster,rsquo;rsquo; held together by the anisotropic quadrupolendash;quadrupole interactions. At 3 K the three moleculeJ=1 cluster is dissolved within the (D2)13cluster. The orientational structure of the (parahyphen;D2)13cluster at 1 K is composed of two distinct distortedhyphen;T pair configurations of neighboringJ=1 molecules. Upon heating to 3 K the orientational structure changes, and a clear separation between the two pair geometries is no longer obtained. Moreover at 3 K thermal distortion of the cluster structure from icosahedral relaxes the extent of orientational frustration of the system, and thus contributes to the lowering of the rotational energy.
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