Measurements of pressure-induced infrared frequency shifts and a theory of liquids based on hindered molecular vibration

A new approach to the liquid state has been attempted. The stretching vibrational frequency of molecules changes when molecules are condensed from the gaseous phase to the liquid phase, or compressed to a higher density in the same phase. The frequency shift of the molecule indicates the intermolecular interactions between the molecule and all surrounding molecules within the effective range of the intermolecular forces. A high resolution and precision infrared spectrophotometer and a high pressure infrared cell were designed, constructed and calibrated for static measurements of frequency shifts at various pressures. The transmittance of each absorption band was measured at the static condition of the monochromator, and fitted to a simplified Lorentz equation from which the minimum of the band was determined. A digital computer was used in the processing of data. With this specially developed technique, the precision of frequency measured was increased to one hundredth of a wave number. A relationship between the frequency shift and the self-consistent potential field in which the molecule vibrates was derived. Also equations were derived to calculate thermodynamic properties from the frequency shift. [...]