Structure and thermal expansion of α‐CO

X‐ray diffraction studies have been carried out on carbon monoxide in the temperature range of 8 to 63 °K. The analysis of the Bragg reflection intensity has shown that the α‐CO structure belongs to the space group Pa3. From the data of the temperature dependence of the lattice parameter the molar volume thermal expansion coefficient has been calculated and the heat capacity C_v and Grüneisen coefficient γ were found. The heat capacity component C_vlib due to angular vibrations of the molecules has been separated. The temperature dependence found for C_vlib and γ is in good agreement with that calculated in the molecular field approximation for a libron subsystem of the crystal, where anharmonic librations and lattice thermal expansion are taken into account.