Volume 83, Number 6, September 2008
Article Number 66008
Number of page(s) 6
Section Condensed Matter: Structural, Mechanical and Thermal Properties
Published online 12 September 2008
EPL, 83 (2008) 66008
DOI: 10.1209/0295-5075/83/66008

Infrared Q-branch anomalies on cooling small OCS (pH2)n clusters from 0.38 K to 0.15 K

S. Grebenev, B. G. Sartakov, J. P. Toennies and A. F. Vilesov

 Max-Planck-Institut für Dynamik und Selbstorganisation - Bunsenstraße 10, 37073 Göttingen, Germany, EU

received 26 May 2008; accepted in final form 25 July 2008; published September 2008
published online 12 September 2008

Infrared spectra of OCS molecules with 8 $\leq$ n $\leq$ 16 attached para-hydrogen (pH2) molecules inside pure 4He droplets at 0.38 K and in mixed 4He/3He droplets at 0.15 K are compared with the same-sized oD2 clusters. In the pH2 clusters the Q-branch is observed at 0.38 K, except for n = 12, but disappears for n $\geq$ 11 on cooling to 0.15 K, whereas it is present in all the oD2 clusters. The high axial symmetry of the pH2 clusters at 0.15 K is consistent with the onset of microscopic superfluidity resulting predominantly from exchanges accompanying the hindered rotations of two or more rings.

67.90.+z - Other topics in quantum fluids and solids.
36.40.Mr - Spectroscopy and geometrical structure of clusters.
33.20.Ea - Infrared spectra.

© EPLA 2008