INFRARED INTENSITIES OF LIQUIDS .19. A SIMPLE AND EFFECTIVE APPROXIMATE METHOD FOR THE CALCULATION OF INFRARED OPTICAL-CONSTANT SPECTRA OF LIQUIDS FROM TRANSMISSION MEASUREMENTS

A simple and effective approximate method is presented for the calcula tion of the optical constants of neat liquids from transmission measur ements. The method calculates the apparent absorbance due to reflectio n losses by treating the liquid cell as a single slab of the window ma terial. This approach makes the method far simpler than the exact iter ative method that has been used to develop secondary infrared intensit y standards and that applies Fresnel's equations to each interface in the cell. However, for all but the strongest absorption bands, the app roximate method gives imaginary refractive indices that are within sim ilar to 1% of those from the exact method. The method is, thus, useful for nearly all common liquids in cells with alkali halide windows for all but the strongest bands. The effect of the size of the mismatch b etween the real refractive indices of sample and windows has been expl ored to some extent. It is recommended that results from the approxima te method be regarded with caution if the refractive indices of the sa mple and windows differ by more than 0.15.