Effect of the symmetry of H2 molecules on their rotations around an OCS molecule in superfluid4He droplets

The infrared spectra of OCS-(H 2 ) n clusters in cold (0.15 K) superfluid 4 He droplets coated with 3 He exhibit resolved rotational bands for each n up to n = 8 para-H 2 (pH 2 ) or ortho-D 2 (oD 2 ) molecules. An analysis ofthe different Q-branch intensities based on the different spin symmetries of pH 2 and oD 2 indicates the formation of symmetric 5- or 6-membered rings around the linear carbonyl sulfide (OCS) chromophore. The rings of distinguishable oD 2 are found to undergo axial rotations, whereas for 6 pH 2 molecules the symmetry-allowed rotational levels lie too high to be excited at the 0.15 K droplet temperatures.