Figure 1 Temperature-dependent Raman frequency of (a) the intramolecular nonbonding lone pair O2- : H+/p (wL < 350 cm-1) and (b) the intermolecular bonding pair O2--H+/p (wH > 3000 cm-1) shows the melting point at T > 268 K. Despite the phase transitions, the Raman shifts of the two modes indicate the opposite relaxation of the nonbonding and bonding electron pairs.