<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mi>λ</mml:mi></mml:math>Anomaly in the Heat Capacity of Solid Hydrogen at Small Molar Volumes

Abstract

Apparatus for the determination of properties of solid hydrogen at volumes between 15 and 23 cc/mole is described. The results of measurements on the $\ensuremath{\lambda}$ anomaly in the heat capacity of solid hydrogen containing large concentrations of orthohydrogen are reported for molar volumes from 15.8 to 22.6 cc. The $\ensuremath{\lambda}$ temperature was found to vary with intermolecular separation $R$ as ${R}^{\ensuremath{-}5}$, with a small contribution from a higher exponent. This is in agreement with the expected relative contributions of electric quadrupole and valence interactions to the intermolecular potential. The relative contribution of the $\ensuremath{\lambda}$ anomaly to the total anomalous entropy was estimated. The $\ensuremath{\lambda}$ anomaly was found to have at least two distinct peaks.