A Theoretical Model For Wide-band Infrared-absorption Molecular Spectra At Any Pressure: Fiction Or Reality?

Various atmospheric applications require modeling of infrared absorption by the main atmospheric species in wide ranges of frequencies, pressures and temperatures. For different pressure regimes, different mechanisms are responsible for the observed intensities of vibration-rotation line manifolds, and the structure of the bands changes drastically when going from low to high densities. Therefore, no universal theoretical model exists presently to interpret simultaneously collACSed band-shapes observed at very high pressures and isolated-line shapes recorded in sub-atmospheric regimes. Using CO$_2$ absorption spectra as an example, we introduce some improvements in the non-Markovian Energy-Corrected Sudden model, developed for high-density spectra of arbitrary tensorial rank\footnote{J.V. Buldyreva and L. Bonamy, Phys. Rev. A 60(1), 370-376 (1999).} and generalized recently to parallel and perpendicular infrared absorption bands\footnote{J. Buldyreva and L. Daneshvar, J. Chem. Phys. 139, 164107 (2013).}, and test the applicability of this approach for the case of nearly Doppler pressure regime via comparisons with recently recorded experimental intensities\footnote{L. Daneshvar, T. F\"{o}ldes, J. Buldyreva, J. Vander Auwera, J. Quant. Spectrosc. Radiat. Transfer 2014 (to be submitted).}