Thermal expansion of solid methane and conversion processes

The thermal expansion of pure solid methane, methane containing oxygen and nitrogen impurities, and a solid solution of 75% CH4 + 25% CD4 was investigated in the temperature range 2−4°K. The temperature dependence of thermal expansion in methane of equilibrium spin modification composition was determined. The connection between the negative thermal expansion coefficient of methane and conversion processes was established experimentally, in qualitative agreement with the basic conclusions of the theoretical studies by Yamamoto and coworkers. Characteristic conversion times and their temperature dependence above 5.8°K were derived from the analysis of the variation in time with changing temperature of the dimensions of pure methane specimens. It was found that O2 and N2 impurities affect considerably the thermal expansion of methane of equilibrium spin modification composition. The orientationally disordered sublattices turned out to be more sensitive to the effect of impurities. An explanation is suggested for the influence of impurities with quadrupole intermolecular interaction on the thermal expansion of methane. A study of the methane-deuteromethane solution permitted us to find distinctive features of thermal expansion in the orientationally ordered phase of CH4.

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