title: OCS in para-hydrogen clusters: rotational dynamics and superfluidity.
abstract: We present a detailed analysis of the rotational excitations of the linear OCS molecule solvated by a variable number of para-hydrogen molecules (9 < or = N < or = 17). The effective rotational constant extracted from the fit of the rotational energy levels decreases up to N = 13, indicating near-rigid coupling between OCS rotations and para-hydrogen motion. Departure from rigidity is instead seen for larger clusters with 14 < or = N < or = 17. Path-integral Monte Carlo calculations show that the N dependence of the effective rotational constant can be explained in terms of a partial superfluid response of para-hydrogen to rotations about an axis perpendicular to the OCS axis. Complete para-hydrogen superfluid response to rotations about the OCS axis is found for N > or = 10.
authors.affiliation: Department of Chemistry and Pitzer Center for Theoretical Chemistry, University of California, Berkeley, California 94720, USA. fpaesani@holmium.cchem.berkeley.edu
authors.forename: F
authors.initials: F
authors.lastname: Paesani
authors.forename: R E
authors.initials: RE
authors.lastname: Zillich
authors.forename: Y
authors.initials: Y
authors.lastname: Kwon
authors.forename: K B
authors.initials: KB
authors.lastname: Whaley