Dielectric Constant Anomaly of CO near its Liquid-Vapor Critical Point

The first observation of the predicted anomaly in the static dielectric constant of a pure fluid near its critical point is reported. This anomaly, not observed to date in nonpolar fluids, is now seen in CO, a polar fluid. The anomalous increase in the dielectric constant, $\frac{\delta \epsilon }{\epsilon }$, reaches 1×${10}^{-3\mathrm{}}$ for fluid with density very close to the critical value. The functional form of the anomaly is consistent with current theoretical predictions.