One of the elementary models of molecular band absorption is the quasi-random model. This model is used to study the propagation of a laser beam through vapor media. 1.15μm is one of the many helium-neon lasers operating in the near-IR region; in this region water vapor molecules have five absorption lines. Absorption of this laser beam in a cloud of water vapor, in the frequency interval 8676-8680 cm-1, is shown in intervals 0.2 cm-2 wide for two different path lengths. Interaction of a tunable dye laser beam with p-benzoquinone-D4 lines is studied in the frequecny range 20750-22275 cm-1. Values of transmittance, averaged over intervals of 25 cm-1, are obtained for two different absorber thicknesses. From these values, intensities of the absorption lines are simulated.© (2003) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.