Solidification of hydrogen clusters including a foreign molecule

The solidification of small parahydrogen clusters containing a foreign, nonspherical molecule at their centre (in particular OCS, as in the important Gottingen superfluidity experiment), is studied. The foreign molecule (a) partly replaces the solid phase, (b) imposes a nonspherical symmetry to the solid-liquid interface, (c) furnishes a template for solidification, (d) promotes solidification via its van der Waals attraction. By far the most important is the last-mentioned effect (at least for a strongly interacting molecule such as OCS). As a result, the solidification times are drastically reduced with respect to the case of pure hydrogen clusters. Some relationship with the experiment is discussed.