This infrared investigation of organo-phosphorus compounds correlates certain group frequencies Table I contains the groups investigated and the resulting data. [Table 1] The frequency shifts of these vibration with different substituents on the phosphorus atom are discussed.
R. A. Nyquist, "Infrared Spectra of Organo-Phosphorus Compounds: New Correlations," Appl. Spectrosc. 11, 161-164 (1957)