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Fourier Transform Microwave Spectroscopy of Doped Helium Clusters

  1. Wolfgang Jäger,
  2. Yunjie Xu

Published Online: 15 SEP 2011

DOI: 10.1002/9780470749593.hrs034

Handbook of High-resolution Spectroscopy

Handbook of High-resolution Spectroscopy

How to Cite

Jäger, W. and Xu, Y. 2011. Fourier Transform Microwave Spectroscopy of Doped Helium Clusters. Handbook of High-resolution Spectroscopy. .

Author Information

  1. University of Alberta, Department of Chemistry, Edmonton, Alberta, Canada

Publication History

  1. Published Online: 15 SEP 2011


In this article, we describe investigations of rotational spectra of complexes and clusters containing helium atoms. These systems are of much interest mainly because of their very low binding energies and the associated relatively large zero-point energies. As a result, these very weakly bonded systems undergo large amplitude internal stretching and bending motions and the semirigid rotor Hamiltonian can often not describe the spectra appropriately. Microwave spectra of clusters of the type HeN-linear molecule are discussed. The number of helium atoms in the cluster, N, ranges from 1 up to 39 in the case of HeN-carbonyl sulfide. It was possible to record transitions of clusters of successively increasing size and to extract spectroscopic parameters of clusters with atom-by-atom resolution. Probably the most significant outcome from these studies is the observation of an increase in the rotational constant, B, with increasing N. This turnaround occurs at relatively small numbers of helium atoms, e.g., N = 9 for HeN-OCS. The corresponding decrease in moment of inertia with increasing N is attributed to a decoupling of helium density from the rotational motion of the dopant molecule. This is interpreted in terms of the occurrence of superfluid effects on the microscopic scale. Throughout the article, we emphasize the importance of our colleagues in infrared spectroscopy and theory collaborating in this research endeavor.


  • cluster spectroscopy;
  • doped helium clusters;
  • superfluidity;
  • microscopic superfluidity;
  • rotational spectra;
  • nuclear quadrupole coupling;
  • helium nanodroplets