This document is subject to special export controls and each transmittal to foreign governments or foreign nationals may be made only w*ta prior approval of the Office of Naval Research (Code 421), WILLOW RUN LABORATORIES ACKNOWLEDGMENTS The author wishes to acknowledge the assistance of Harvey M. Rose, who provided first-draft versions of sections 4, 5, and 6, and who contributed largely to the many computational and plotting labors encountered in the writing of this report. I am particularly indebted to George Oppel for his technical advice and suggestions, and for providing the necessary information for section 2.3. ABSTRACT The general transmissivity equation for computing slant-path molecular absorption spectra is developed and two methods for evaluating this equation, the direct integration and that which assumes a model of the band structure, are discussed. Five band models are discussed and twelve methods for computing molecular absorption b&sed on these band models are presented. Spectra computed by band-model nethods are compared with spectra calculated by direct integration of the general transmissivity equation and with open-air field measurements of absorption spectra. Conclusions concerning the capability of band-model methods for predicting slant-path absorption spectra are stated and recommendations for future research are outlined. A summary of open-air field measurements of absorption spectra and laboratory measurements of absorption spectra for homo geneous paths is presented and a computer program for computing the equivalent sea-level path, the Curtis-Godson equivalent pressure, and the absorber concentration for atmospheric slant paths for any model atmosphere is given in appendix I.