Thermodynamic Properties of Condensed CO

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Abstract
Thermodynamic properties (heat capacities; vapor pressures; heats of transition, fusion, and vaporization) of condensed CO containing 2.6±0.4% N2 have been measured between 2.5° and 78°K. No anomalies nor unusual thermal behavior were observed at the lowest temperatures. The dielectric constant of the pure solid has been measured between 6°K and the melting point and found to be close to unity over the entire temperature range. The residual entropy of CO is discussed in the light of these results. The N2 impurity displaces the melting and solid transition regions to lower temperatures but does not appear to alter their forms. Analyses of the vapor‐pressure data show that the liquid solution of N2 in CO is nearly an ideal one. Deviations from ideality occur in the solid phases, particularly in the α phase that exists in the region T−1 on the librational frequency. This is to be compared with an average value of 70 cm−1 estimated from the optical spectrum of the crystal.