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Spectroscopy of (Helium) N -Molecule Clusters: Tracing the Onset of Superfluidity

Spectroscopy of (Helium) N -Molecule Clusters: Tracing the Onset of Superfluidity. Wolfgang Jäger, Wendy Topic, and Yunjie Xu Department of Chemistry, University of Alberta, Edmonton, AB Canada. Collaborations: Bob McKellar, Jiang Tang, NRC (mid-IR) PN Roy, Nick Blinov, UofA (theory).

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Spectroscopy of (Helium) N -Molecule Clusters: Tracing the Onset of Superfluidity

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  1. Spectroscopy of (Helium)N-Molecule Clusters: Tracing the Onset of Superfluidity Wolfgang Jäger, Wendy Topic, and Yunjie Xu Department of Chemistry, University of Alberta, Edmonton, AB Canada Collaborations: Bob McKellar, Jiang Tang, NRC (mid-IR) PN Roy, Nick Blinov, UofA (theory)

  2. From the Molecular Regime to the Bulk Phase

  3. A Case in Point: Superfluidity • 4He becomes superfluid below the λ-point (2.17 K) • Frictionless flow, irrotationality, quantized vorticity, fountain effect … Andronikashvili experiment ‘Drag’ from normal fluid component causes increase of moment-of-inertia of disk stack. Confirmation of two fluid model.

  4. The Microscopic Andronikashvili Experiment Grebenev, Toennies, Vilesov, Science279, 2083 (1998).

  5. The Small Cluster Approach

  6. Rotational (microwave) spectra of HeN-molecule clusters. Clusters are produced in pulsed molecular expansion. Instrument: FT Microwave Spectrometer, 4 - 26 GHz (~0.1 - 1 cm-1).

  7. HeN – Molecule Clusters 1. HeN-OCS (N=1-8)

  8. Multidimensional Assignment Procedure a) infrared predictions b) sample conditions (pressure, temperature) c) double resonance experiments d) consistency of isotopic data e) spectral fits

  9. Vibrational Frequency Shifts of HeN-OCS Clusters experimental values, Tang, Xu, McKellar, Jäger, Science297, 5030 (2002). Helium droplet value values from Whaley and co-workers, JCP115, 10225 (2001).

  10. Spectroscopic Constants of HeN-OCS Clusters

  11. Proposed Structure of He8-OCS

  12. Helium density in He8-OCS P. N. Roy, N. Blinov, private communication.

  13. Rotational Constant vs.Number of He Atoms

  14. … and very recent Calculations. N. Blinov, X. Song, P. N. Roy, JCP120, 5916 (2004). S. Moroni et al., Phys. Rev. Lett.90, 143401 (2003).

  15. Helium Density Profiles in HeN-OCS N=6 N=5 N=8 N=7 N=10 N=9 N. Blinov, X. Song, P. N. Roy, JCP120, 5916 (2004).

  16. 2. HeN-N2O (N=1-19)

  17. Potential Energy Surface of He-N2O level of theory: CCSD(T) basis set: aug-cc-pVTZ bond functions: 3s, 3p, 2d, 1f, 1g Energies in cm-1 X. Song, P. N. Roy, Y. Xu, and W. Jäger, submitted.

  18. Bound State Calculations for He-N2O

  19. J=1-0 Rotational Transition He5-14N15NO Intensity 6792.0 6793.5 He7-14N15NO Intensity 5471.5 5473.0 He12-14N15NO Intensity 6194.5 6195.5 Xu, Jäger, Tang, McKellar, Phys. Rev. Lett. 91, 163401 (2003). Frequency / MHz

  20. He6-N2O in its Principal Inertial Axes System

  21. Rotational Constant vs.Number of He Atoms Helium droplet value Nauta, Miller, JCP115, 10254 (2001.) S. Moroni, N. Blinov, P. N. Roy, JCP, accepted.

  22. Helium Density Distributions in HeN-N2O N=6 N=5 N=10 N=9 N=15 N=14

  23. Our Plan for the Future • Push to even larger cluster sizes (N~60?). • Use non-linear dopant molecules. • (H2)N-molecule systems (already in progress).

  24. Acknowledgements Dr. Dominik Bremm Dr. Aiko Huckauf Dean Court Dr. Yaqian Liu Dr. Silas Ngari Dr. Hans Osthoff Dr. Jennifer van Wijngaarden Kai Brendel Jen Landry Qing Wen Kyle Green Kristine Liao James Song Ling Tang Bilkiss Issack Dr. Nick Blinov Dr. Bob McKellar Dr. PN Roy Chemistry Design and Manufacturing Facility NSERC ASRA, ISRIP CIPI Faculty of Science, UofA $$$

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