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Title: Recurrences in rotational dynamics and experimental measurement of superfluidity in doped helium clusters

Abstract

We present the first experimental evidence of recurrences in the rotational dynamics of doped helium clusters. Using the dopant molecule as an experimental microscopic probe of superfluidity, we show that in small He{sub N}-N{sub 2}O complexes, superfluidity builds up in stages correlated with the filling and completion of a solvation shell.

Authors:
; ; ;  [1]
  1. Department of Chemistry, University of Alberta, Edmonton, Alberta, T6G 2G2 (Canada)
Publication Date:
OSTI Identifier:
20783233
Resource Type:
Journal Article
Resource Relation:
Journal Name: Journal of Chemical Physics; Journal Volume: 124; Journal Issue: 8; Other Information: DOI: 10.1063/1.2173640; (c) 2006 American Institute of Physics; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
37 INORGANIC, ORGANIC, PHYSICAL AND ANALYTICAL CHEMISTRY; 74 ATOMIC AND MOLECULAR PHYSICS; ATOMIC CLUSTERS; COMPLEXES; DOPED MATERIALS; HELIUM; MOLECULES; NITROUS OXIDE; PROBES; ROTATIONAL STATES; SOLVATION; SUPERFLUIDITY

Citation Formats

Xu Yunjie, Blinov, Nicholas, Jaeger, Wolfgang, and Roy, Pierre-Nicholas. Recurrences in rotational dynamics and experimental measurement of superfluidity in doped helium clusters. United States: N. p., 2006. Web. doi:10.1063/1.2173640.
Xu Yunjie, Blinov, Nicholas, Jaeger, Wolfgang, & Roy, Pierre-Nicholas. Recurrences in rotational dynamics and experimental measurement of superfluidity in doped helium clusters. United States. doi:10.1063/1.2173640.
Xu Yunjie, Blinov, Nicholas, Jaeger, Wolfgang, and Roy, Pierre-Nicholas. Tue . "Recurrences in rotational dynamics and experimental measurement of superfluidity in doped helium clusters". United States. doi:10.1063/1.2173640.
@article{osti_20783233,
title = {Recurrences in rotational dynamics and experimental measurement of superfluidity in doped helium clusters},
author = {Xu Yunjie and Blinov, Nicholas and Jaeger, Wolfgang and Roy, Pierre-Nicholas},
abstractNote = {We present the first experimental evidence of recurrences in the rotational dynamics of doped helium clusters. Using the dopant molecule as an experimental microscopic probe of superfluidity, we show that in small He{sub N}-N{sub 2}O complexes, superfluidity builds up in stages correlated with the filling and completion of a solvation shell.},
doi = {10.1063/1.2173640},
journal = {Journal of Chemical Physics},
number = 8,
volume = 124,
place = {United States},
year = {Tue Feb 28 00:00:00 EST 2006},
month = {Tue Feb 28 00:00:00 EST 2006}
}
  • In this paper, quantum fluctuations of a carbonyl sulfide molecule in helium-4 clusters are studied as a function of cluster size N in a small-to-large size regime (2{<=}N{<=}64). The molecular rotation of the dopant shows nonmonotonic size dependence in the range of 10{<=}N{<=}20, reflecting the density distribution of the helium atoms around the molecule. The size dependence on the rotational constant shows a plateau for N{>=}20, which is larger than the experimental nanodroplet value. Superfluid response of the doped cluster is found to show remarkable anisotropy especially for N{<=}20. The superfluid fraction regarding the axis perpendicular to the molecular axismore » shows a steep increase at N=10, giving the significant enhancement of the rotational fluctuation of the molecule. On the other hand, the superfluid fraction regarding the axis parallel to the molecular axis reaches 0.9 at N=5, arising from the bosonic exchange cycles of the helium atoms around the molecular axis. The anisotropy in the superfluid response is found to be the direct consequence of the configurations of the bosonic exchange cycles.« less
  • It is shown by computer simulations that superfluid parahydrogen clusters of more than 22 molecules can be turned insulating and 'solidlike' by the replacement of as few as one or two molecules, with ones of the heavier orthodeuterium isotope. A much smaller effect is observed with substitutional orthohydrogen. Substitutional orthodeuterium molecules prevalently sit in the inner part of the cluster, whereas orthohydrogen impurities reside primarily in the outer shell, near the surface. Implications on the superfluidity of pure parahydrogen clusters are discussed.
  • In this paper we present calculations of electron tunneling times from the ground electronic state of excess electron bubbles in ({sup 4}He){sub N} clusters (N=6500-10{sup 7}, cluster radius R=41.5-478 A ), where the equilibrium bubble radius varies in the range R{sub b}=13.5-17.0 A. For the bubble center located at a radial distance d from the cluster surface, the tunneling transition probability was expressed as A{sub 0}{phi}(d,R)exp(-{beta}d), where {beta}{approx_equal}1 A {sup -1} is the exponential parameter, A{sub 0} is the preexponential factor for the bubble located at the cluster center, and {phi}(d,R) is a correction factor which accounts for cluster curvaturemore » effects. Electron tunneling dynamics is grossly affected by the distinct mode of motion of the electron bubble in the image potential within the cluster, which is dissipative (i.e., {tau}{sub D}<{tau}{sub 0}) in normal fluid ({sup 4}He){sub N} and ({sup 3}He){sub N} clusters, while it is undamped (i.e., {tau}{sub D}>>{tau}{sub 0}) in superfluid ({sup 4}He){sub N} clusters, where {tau}{sub D} is the bubble motional damping time ({tau}{sub D}{approx_equal}4x10{sup -12} s for normal fluid clusters and {tau}{sub D}{approx_equal}10 s for superfluid clusters), while {tau}{sub 0}{approx_equal}10{sup -9}-10{sup -10} s is the bubble oscillatory time. Exceedingly long tunneling lifetimes, which cannot be experimentally observed, are manifested from bubbles damped to the center of the normal fluid cluster, while for superfluid clusters electron tunneling occurs from bubbles located in the vicinity of the initial distance d near the cluster boundary. Model calculations of the cluster size dependence of the electron tunneling time (for a fixed value of d=38-39 A ), with lifetimes increasing in the range of 10{sup -3}-0.3 s for N=10{sup 4}-10{sup 7}, account well for the experimental data [M. Farnik and J. P. Toennies, J. Chem. Phys. 118, 4176 (2003)], manifesting cluster curvature effects on electron tunneling dynamics. The minimal cluster size for the dynamic stability of the bubble was estimated to be N=3800, which represents the threshold cluster size for which the excess electron bubble in ({sup 4}He){sub N}{sup -} clusters is amenable to experimental observation.« less
  • Discrete visible and near-infrared luminescence of a beam of photoexcited helium clusters is reported. The emission lines are attributed to free helium atoms and molecules desorbing from clusters in electronically excited states. Depending on the excitation energy, various atomic and molecular singlet and triplet states are involved in the relaxation process. With increasing cluster size the intensity of molecular transitions becomes dominant. The temperature of ejected molecules could be estimated to T{sub vib}{approximately}2500 K and T{sub rot}{approximately}450 K and is much higher than that of the cluster itself. {copyright} {ital 1997} {ital The American Physical Society}