15min:

B. SARTAKOV, General Physics Institute RAS, Vavilov str. 38, 119991 Moscow, Russia; A. VILESOV, Department of Chemistry, University of Southern California, Los Angeles, CA 90089, USA; AND J. PETER TOENNIES, Max-Planck-Institut fur Stromungsforschung, Bunsenstrasse 10 37073 Goettingen, Germany .

Rotationally resolved IR spectra of molecules and hydrogen clusters trapped in ⁴He and mixed ³He/⁴He droplets are presented. The newest analysis of spectra in terms of effective rotational constants of OCS-(pH₂)_n and OCS-(oD₂)_n complexes with n=11,\dots16 is presented. Whereas molecular rotation in ⁴He can be modelled by a free rotor with effective rotational constants the effect of interaction between a molecule and its H₂ solvation shell is more pronounced. Analysis of the spectra within the frameworks of a rigid symmetric H₂ shell proves the inconsistency of the rigid shell model with the experimental observations. Furthermore it suggests existence of some low energy excitations (E 0.1~cm^-1) which are tentatively assigned to tunnelling states of the H₂ cluster.