Rotational spectroscopy of single carbonyl sulfide molecules embedded in superfluid helium nanodroplets

The pure rotation spectrum of carbonyl sulfide embedded in superfluid helium nanodroplets was measured in the frequency range from 4 to 15.5 GHz. Four lines, corresponding to the J = 1-0, J = 2-1, J = 3-2, and J = 4-3 transitions, were found. The line widths of the transitions increase with increasing rotational quantum number J, which is indicative of a distribution of the effective B rotational constant. A comparison of the pure rotational spectrum with the microwave-infrared double resonance spectrum [S. Grebenev, M. Havenith, F. Madeja, J. P. Toennies, and A. F. Vilesov, J. Chem. Phys., 2000, 113(20), 9060] reveals that the double resonance measurement scheme probes predominantly rotational transitions within the vibrationally excited state.