A high electric field impedance experiment on supercooled molecular liquids is employed to transfer energy to the slow modes by absorption from the field and detect the increase of their “configurational temperature”, $T_{\mathrm{cfg}}$, via the change of the relaxation times. This allows us to determine the configurational heat capacity, which accounts for most of the excess heat capacity for stronger liquids, but for only half of the heat capacity step in the case of more fragile systems. It is also observed that $T_{\mathrm{cfg}}$ gradually approaches the phonon temperature on the structural relaxation time scale.

• Received 20 June 2007

DOI:https://doi.org/10.1103/PhysRevLett.99.185701