The anomalous temperature variation of the symmetric stretching vibration νs(H2O) in hexa‐aqua metal (II) hexafluorosilicate (IV)

The anomalous temperature dependence of the linewidth of the νs(H2O) symmetric stretch vibration in hexa‐aquo metal (II) hexafluorosilicate (IV) salts is discussed in terms of anharmonic interactions. It is shown that the main contribution to the linewidth is an elastic scattering process between νs(H2O) and the torsional vibration of the water molecules leading to a pure vibrational dephasing. Contributions to the linewidth due to inelastic decay into other vibrational states are also discussed.