Superfluidity of Monolayer Helium Films

The paper gives the results of studies and analysis of the behavior of the thermal expansion coefficient of the Ar–-O₂solid solutions containing 0.27, 0.52 and 1.02 mol% of O₂. Contributions of single oxygen molecules and clusters consisting of 2 and 3 molecules of O₂to the thermal expansion have been determined. It has been found that the clusters consisting of two oxygen molecules contribute mainly to the thermal expansion of these solid solutions at temperatures below 5 K. The contribution of single molecules of oxygen becomes negative at temperatures below 5.5 K.