A concealed anomaly at 117.5 K in the heat capacity of hexamethylbenzene

摘要: Heat capacities of solid hexamethylbenzene were measured in an adiabatic calorimeter between 3 and 300 K with particular attention to the phase transition at 117 III II. The is very likely be first order temperature 117.5±0.1 K, heat 0.99±0.02 kJ mol−1, entropy 8.3±0.2 J K−1 mol−1. reason why has been referred as a λ because there additional thermal anomaly concealed behind transition, which maximum large 50 J K−1 mol−1 128 K. This anomaly, or hump capacity curve, was interpreted terms rotatory oscillation/hindered rotation methyl groups potential barrier shape V = V3 cos 3ϑ+V6 cos 6ϑ+V9 cos 9ϑ V3 4×10−21 J, V6 1×10−21 V9 3×10−21 J. effect on merely cause small jump otherwise continuous beginning through A term, excitati...