Figure 2: Detection of ortho–para conversion in H₂O@C₆₀.

(a) Photograph and (b) exploded view of the sample cell consisting of two printed circuit boards (PCBs, green) and a 210 μm thick G10 spacer used to centre the sample pellets between the electrodes of the two PCBs, forming three independent capacitor cells. Scale bar length in a is 2 cm. Following a temperature jump from 25 to 5 K at the time origin, the capacitance of the three cells is measured as a function of time. (c) The capacitance of the cell loaded with H₂O@C₆₀ decreases monotonically due to ortho–para conversion. The capacitances of (d) the empty cell and (e) the cell loaded with C₆₀ change slightly as the temperature is changed, but are constant after the temperature jump. The temperature measurement is shown in f.