A simplified equation for attenuated total reflection (ATR) spectral intensity in a three-phase system under a small absorption condition is derived. The spectral intensity is expressed in terms of a linear function of the bulk spectral intensities or absorption coefficients of the absorbing media. The applicability and limitation of the simplified equation are verified by comparing the spectral intensity obtained from the simplified equation to that from the exact equation.
Sanong Ekgasit and Heinz W. Siesler, "Simplified Equation for ATR Spectral Intensity of a ThreePhase System," Appl. Spectrosc. 52, 367-374 (1998)