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This talk reviews our recent experiments with cryogenic beams of helium and hydrogen droplets. Rotational-vibrational spectra in series of light tetrahedral molecules such as CH4, CD4, SiH4 and SiD4 reveal the dependence of the coupling of the embedded molecules with liquid helium environment on the speed of molecular rotation. Then, experiments aimed at observation of superfluidity in para-hydrogen will be discussed. Large para-H2 clusters are obtained in a cryogenic pulsed free jet expansion, and nonlinear Raman spectroscopy was used to determine their aggregate state. The results show that clusters formed of highly diluted para-H2 in He remain liquid at estimated temperatures of about or less than 2 K, i.e., close to predicted superfluid transition temperature. Results on mixed ortho-H2 /para-H2 clusters will also be presented. |
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