Ab Initio Calculations of Infrared Absorption Cross Sections of CO₂ Gas

An ab initio model is used to determine the infrared absorption cross sections of CO₂ gas as a function of laser wavelength. The intra-molecular potential energy and electric dipole moment of the CO₂ molecule as a function of molecular nuclear configurations are obtained by solving the Kohn-Sham (KS) equation. The rotational constants at different vibrational levels, the vibrational energy eigen values and transition dipole moments are determined by solving the pure vibrational Schrödinger equation. Using the Fermi\u27s Golden Rule and all the calculated ab initio results, the absorption cross sections of CO₂ gas at room temperature and one atmosphere pressure are obtained. The calculated results have a good agreement with experimental results. Based on the calculated ab initio results, the infrared absorption cross sections of CO₂ gas at higher pressures are calculated. The absorption spectra at high pressures are found to be much smoother due to the overlaps between neighboring absorption line shapes. Copyright © 2008 by ASME