Discrete Visible Luminescence of Helium Atoms and Molecules Desorbing from Helium Clusters: The Role of Electronic, Vibrational, and Rotational Energy Transfer

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Abstract
Discrete visible and near-infrared luminescence of a beam of photoexcited helium clusters is reported. The emission lines are attributed to free helium atoms and molecules desorbing from clusters inelectronically excited states. Depending on the excitation energy, various atomic and molecularsinglet and triplet states are involved in the relaxation process. With increasing cluster size theintensity of molecular transitions becomes dominant. The temperature of ejected molecules couldbe estimated to Tvib,2500K and Trot,450K and is much higher than that of the cluster itsel