Since vibrational frequency shifts in liquids, produced by solvents and/or high liquid densities, are relatively small, precision equipment and techniques must be used. Design and operation of modified equipment, including a long path grating monochromator, a pressuring system and cells for pressures up to 5000–10000 atm are described. A static measurement technique, involving precise positioning of the grating and read out of the transmittance on a digital voltmeter, followed by computer processing of the series of points which describe the absorption peak to determine the ν0, are also described. Experimental data on C=C vibration on cis-pentene-2 are presented to illustrate results.
C. S. Fang, J. V. Fox, C. E. Mauk, and H. W. Prengle, "Equipment for High-Pressure Infrared Measurements," Appl. Spectrosc. 24, 21-27 (1970)