SUPERFLUID EFFECTS IN PARA-H$_2$ CLUSTERS PROBED BY CO$_2$ ROTATION-VIBRATION TRANSITIONS
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Date
2010
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Publisher
Ohio State University
Abstract
The prospect of directly observing superfluidity in para-H$_2$ is a tantalizing but elusive goal. Like $^4$He, para-H$_2$ is a light zero-spin boson. However, H$_2$-H$_2$ intermolecular interactions, though weak, are stronger than He-He interactions, and hydrogen is a solid below about 14 K. This makes detection of superfluidity in bulk hydrogen problematical, to say the least. But there are still possibilities for para-H$_2$ in the form of clusters or in nano-confined environments, and superfluid transition temperatures as high as $\sim$6 K have been predicted. \textbf{15}, 343 (1972).} Spectroscopic observations of (para-H$_2$)$_N$-CO$_2$ clusters were at first very difficult to interpret for $N > 5$. However, with the help of path integral Monte Carlo simulations and an accurate new H$_2$-CO$_2$ intermolecular potential surface, submitted.} which explicitly incorporates dependence on the CO$_2$ \nub{3} asymmetric stretch, it is now possible to achieve a remarkably consistent picture of (para-H$_2$)$_N$-CO$_2$ clusters in the size range $N$ = 1 $\sim$ 20. By combining the experimental spectroscopic measurements and theoretical simulations, we determine the size evolution of the superfluid response of the CO$_2$-doped para-H$_2$ clusters, which peaks for the ``magic" number $N$ = 12.
Description
Author Institution: Department of Chemistry, University of Waterloo; Waterloo, ON N2L 3G1, Canada; Steacie Institute for Molecular Sciences, National Research; Council of Canada, Ottawa, ON K1A 0R6, Canada