A time resolved VUV fluorescence study of hydrogen clusters:: evidence of a liquid phase

The mobility of Xe atoms captured from a cross jet by hydrogen clusters is investigated with time resolved VUV fluorescence excitation spectroscopy. A band blue shifted by 0.5 eV with respect to the 5p-->6s transition of free Xe atoms is observed. It is attributed to Xe atoms profoundly embedded in hydrogen dusters and surrounded by several layers of hydrogen. The complete absence of features related to surface sites gives evidence that after the pick up process the xenon atoms penetrate deep into the interior of the hydrogen clusters. This indicates that hydrogen clusters show a liquid-like behavior similar to helium clusters, though their estimated temperature (similar to 6 K) is much below the triple point of hydrogen (14 K). (C) 2000 Elsevier Science B.V. All rights reserved.