MOLECULAR SUPERFLUIDITY IN SMALL CLUSTERS OF ({\em p}H$_2$){\em $_N$}-HCN STUDIED WITH ROTATIONAL SPECTROSCOPY
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Date
2012
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Ohio State University
Abstract
In a recent experimental and theoretical study by Li {\em et al}. {\bf 105}, 133401 (2010).}, direct evidence for molecular superfluidity in small clusters of {\em para}-hydrogen molecules ({\em p}H$_2$) seeded with CO$_2$ was discovered. The authors also found that the anisotropy of the CO$_2$--{\em p}H$_2$ interaction potential promotes localization of the {\em p}H$_2$ molecules at larger cluster sizes ({\em N} $\approx$ 17 {\em para}-hydrogen molecules), with a simultaneous reduction of the superfluid {\em p}H$_2$ fraction. It has been suggested that light rotors with a more isotropic interaction potential, such as CO and HCN, are potentially more subtle probes of {\em p}H$_2$ superfluidity that would allow superfluidity to persist, especially at larger values of {\em N}. In the current study, the hyperfine structures of the end-over-end rotational transitions of ({\em p}H$_2$){\em $_N$}-HCN clusters were measured using our chirped-pulse Fourier transform microwave spectrometer. Based on tentative assignments, the evolution of effective rotational constants, {\em B$_{eff}$}, as a function of {\em N} shows evidence for superfluid behaviour by a clear "turn-around'' point at a low {\em N} value. The trend of {\em B$_{eff}$} vs. {\em N} and the results from the hyperfine structure analysis will be compared to the recent studies on He{\em $_N$}-HCN and ({\em p}H$_2$){\em $_N$}-CO.
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Author Institution: Department of Chemistry, University of Alberta, Edmonton, Canada T6G 2G2