Shapes of rotating normal fluid He3 versus superfluid He4 droplets in molecular beams

Deepak Verma, Sean M. O. O’Connell, Alexandra J. Feinberg, Swetha Erukala, Rico Mayro P. Tanyag, Charles Bernando, Weiwu Pang, Catherine A. Saladrigas, Benjamin W. Toulson, Mario Borgwardt, Niranjan Shivaram, Ming-Fu Lin, Andre Al Haddad, Wolfgang Jäger, Christoph Bostedt, Peter Walter, Oliver Gessner, and Andrey F. Vilesov
Phys. Rev. B 102, 014504 – Published 8 July 2020
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Abstract

Previous single-pulse extreme ultraviolet and x-ray coherent diffraction studies revealed that superfluid He4 droplets obtained in a free jet expansion acquire sizable angular momentum, resulting in significant centrifugal distortion. Similar experiments with normal fluid He3 droplets may help elucidate the origin of the large degree of rotational excitation and highlight similarities and differences of dynamics in normal and superfluid droplets. Here, we present a comparison of the shapes of isolated He3 and He4 droplets following expansion of the corresponding fluids in vacuum at temperatures as low as ∼2 K. Large He3 and He4 droplets with average radii of ∼160 and ∼350 nm, respectively, were produced. We find that the majority of the shapes of He3 droplets in the beam correspond to rotating oblate spheroids, in agreement with previous observations for He4 droplets. The aspect ratio of the droplets is related to the degree of their rotational excitation, which is discussed in terms of reduced angular momenta (Λ) and reduced angular velocities (Ω), the average values of which are found to be similar in both isotopes. This similarity suggests that comparable mechanisms induce rotation regardless of the isotope. We hypothesize that the observed distribution of droplet sizes and angular momenta originates from processes in the dense region close to the nozzle, where a significant velocity spread and frequent collisions between droplets induces excessive rotation followed by droplet fission.

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  • Received 12 March 2020
  • Revised 28 May 2020
  • Accepted 28 May 2020

DOI:https://doi.org/10.1103/PhysRevB.102.014504

©2020 American Physical Society

Physics Subject Headings (PhySH)

Condensed Matter, Materials & Applied PhysicsAtomic, Molecular & OpticalFluid Dynamics

Authors & Affiliations

Deepak Verma1, Sean M. O. O’Connell1, Alexandra J. Feinberg1, Swetha Erukala1, Rico Mayro P. Tanyag1,2, Charles Bernando3,4, Weiwu Pang5, Catherine A. Saladrigas6,7, Benjamin W. Toulson6, Mario Borgwardt6, Niranjan Shivaram8,9, Ming-Fu Lin8, Andre Al Haddad10, Wolfgang Jäger11, Christoph Bostedt10,12, Peter Walter8, Oliver Gessner6,*, and Andrey F. Vilesov1,3,†

  • 1Department of Chemistry, University of Southern California, Los Angeles, California 90089, USA
  • 2Institute for Optics and Atomic Physics, Technical University of Berlin, Berlin 10623, Germany
  • 3Department of Physics and Astronomy, University of Southern California, Los Angeles, California 90089, USA
  • 4School of Information Systems, BINUS University, Jalan K. H. Syahdan No. 9, Kemanggisan, Palmerah, Jakarta 11480, Indonesia
  • 5Viterbi School of Engineering, University of Southern California, Los Angeles, California 90089, USA
  • 6Chemical Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA
  • 7Department of Chemistry, University of California, Berkeley, California 94720, USA
  • 8LCLS, SLAC National Accelerator Laboratory, 2575 Sand Hill Road, Menlo Park, California 94025, USA
  • 9Department of Physics and Astronomy, Purdue University, West Lafayette, Indiana 47907, USA
  • 10Laboratory for Femotochemistry (LSF), Paul Scherrer Institute, Forschungsstrasse 111, 5232 Villigen-PSI, Switzerland
  • 11Department of Chemistry, University of Alberta, Edmonton, Alberta T6G 2G2, Canada
  • 12LUXS Laboratory for Ultrafast X-ray Sciences, Institute of Chemical Sciences and Engineering, École Polytechnique Fédérale de Lausanne (EPFL), CH-1015, Lausanne, Switzerland

  • *ogessner@lbl.gov
  • vilesov@usc.edu

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Issue

Vol. 102, Iss. 1 — 1 July 2020

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