THE CONTROL OF ERRORS IN INFRARED SPECTROPHOTOMETRY .6. THE EVALUATION OF OPTICAL-CONSTANTS BY COMBINED TRANSMISSION AND ATTENUATED TOTAL REFLECTION MEASUREMENTS

An improved technique is described for the determination of the optical constants of liquids in the infrared. It is based on a combination of transmission and attenuated total reflection (ATR) measurements. A novel application of the Kramers-Kronig transform function is involved whereby a single-valued integration constant is derived from a vector of refractive index measurements obtained by ATR. These are measured over a wavenumber range where the absorbance is low. The accuracy of the method is evaluated on the basis of a statistical treatment of the propagation of the estimated errors in the experimentally measured quantities, viz. , the transmittance, the cell thickness, and the ATR measurements which establish the integration constant (anchor point) of the Kramers-Kronig transform function.