X-ray studies of structure and thermal expansion in solid N2

Results of an x-ray study of solid N2 in the temperature range 8–63 °K are presented. By analysis of Bragg reflections it is established that the upper limit of the possible displacement of molecules in α-N2 from centrosymmetric positions does not exceed 0.03 Ǻ. Using data on the temperature dependence of the lattice constant; the density, molecular volume, and coefficient of thermal expansion of the crystal are calculated. Correlation of molecular rotations was found to contribute to the thermal expansion of β–N2 near the phase transition temperature. The values of the heat capacity CV, the Griineisen coefficient, and isothermal compressibility are calculated. The behavior of the component CVrot produced by rotational motion of the molecules, is considered. On the basis of analysis of thermodynamic properties it is proposed that partial molecular ordering is preserved in β-N2.

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