Observation of clustered molecules and ions in liquid iodine

The results of Raman scattering measurements on liquid iodine at elevated temperatures using variable excitation wavelengths are reported. Resonant-enhancement and temperature-dependent spectra indicate additional intramolecular vibrational bands beyond that of I₂ molecules. The presence of a broad, resonantly enhanced, high-frequency, relative depolarized band whose intensity is nonlinear in density suggests the presence of clustered (I₂{)}ₙspecies, such as dimers. A lower-frequency band at ~110{cm}^{{{-}}1}$, which also exhibits resonant enhancement is associated with ${I}₃^- ions. The observation of ions is consistent with the electronic properties of the liquid. The results provide the first evidence for stable clustered species in an elemental diatomic liquid and are consistent with significant intermolecular coupling in liquid and amorphous iodine.