Widom line anomalies

The presence of this Widom line has been proposed to explain low-temperature thermodynamic anomalies. As is evident from the above, the Widom line starts from the critical point where density fluctuation is highest and the fluctuation becomes weaker as the state point goes away from the critical point. 

Some of the anomalies of supercritical fluids can be understood by using the idea of the Widom line. One can then relate, for example, file width of a Raman tine to the temperature- and density-dependent correlation length of the fluid. As we cross the Widom line at constant density, we would expect a sharp rise in the width of the Raman... 

It is interesting to note that the useful properties of supercritical water arise from the breakdown of the extensive HB network that is at least partly responsible for many of the anomalies of liquid water. We have discussed how the use of the idea inherent in the Widom line helps in understanding the large-scale fluctuations observed in supercritical water. Because of the large separation of timescales between vibrational relaxation and density relaxation, the vibrational line widths are influenced significantly by the transient density inhomogeneity present near the critical temperature. 

A typical heat-capacity response is illustrated in Fig. 6 for the case of the T-G phase diagram for various fields, where a line of first-order transitions is terminated at a critical point. For the fields exceeding the critical value, a supercritical evolution is observed along the Widom line [32]. The resulting heat-capacity anomalies are shown for various parts of this diagram together with the corresponding curves of the order parameter, as described by (3) in Sect. 1.1. 

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