The heat capacity of 1D chains of methane molecules in the outer grooves bundles of carbon nanotubes

The heat capacity at constant pressure CP of 1D chains of methane molecules adsorbed into the grooves on the outer surface of the bundles of closed single-walled nanotubes has been measured in the temperature range from 2 to 60 K for the first time. Character of the temperature dependence of CP below 12 K indicates on the presence of Schottky anomaly caused by the tunneling between the lowest energy levels of rotational spectra of A, T, and E-nuclear spin modifications of the methane molecules. Special feature is observed in the area of 14 K, apparently, due to orientational phase transition, in which the nature of the rotational motion of the molecules varies from libration to hindered rotation. It is found that the value of the rotational heat capacity is close to the case of free rotation of the methane molecules in the temperature range of 30-40 K. The increase in derivative dCP(T) / dT above 40 K and peculiarity in the CP(T) near 52 K are due to the processes of decay of 1D chains of CH4. PACS: 65.40.Ba Heat capacity; 65.80.-g Thermal properties of small particles, nanocrystals, nanotubes and other related systems; 68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: Structure and nonelectronic properties; 81.07.De Nanotubes.copy;M.I. Bagatskii, V.V. Sumarokov,and M.S. Barabashko,2016.