Anomalous Behavior in the Vibrational Raman Spectrum of Oxygen under Near-Critical Conditions

The isothermal density dependence of both the shift and width of the Raman $Q$ branch in oxygen gas have been found to exhibit anomalous behavior under near-critical conditions. The observed effects are interpretable in terms of molecular-cluster formation, and it is concluded that the Raman effect is a potentially valuable probe of density fluctuations in the critical region.