The quasi-random model of band absorption provides a means for the accurate representation of molecular absorption over finite frequency intervals. It does not suffer from the limitations of the Elsasser and statistical models. The spacing between actual spectral lines is not constant nor does it vary in a random manner. The essential features of the actual arrangement of these lines are reproduced in the quasi-random model by the division of the frequency interval of interest into much smaller intervals within which the lines are assumed to be arranged at random. The actual intensity distribution including the important effect of the numerous weak lines is accurately simulated. A new expression for the transmittance related to a finite frequency interval is derived. The absorption from the wings of the spectral lines in other intervals is taken into account. Through these and other features the quasi-random model provides a means of accurately representing molecular absorptance over finite frequency intervals.
PHILIP J. WYATT, V. ROBERT STULL, and GILBERT N. PLASS, "Quasi-Random Model of Band Absorption," J. Opt. Soc. Am. 52, 1209-1217 (1962)