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

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

Received: 26 May 2008
Accepted: 25 July 2008

Abstract

Infrared spectra of OCS molecules with 8≤ n ≤ 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 , but disappears for n ≥ 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.