Bond anharmonicities, Gruneisen parameters and pressure-induced frequency shifts

Simple models are used to derive equations that show the inter-relationship between bond anharmonicities and mode Gruneisen parameters. Their reliability is indicated by the accuracy with which they predict recently measured gamma i values from general spectroscopic data. The use of these relationships to define the 'normal behaviour' to be expected for pressure induced frequency shifts is illustrated for simple solids, and their semiquantitative value for more complex structures is indicated.