CALCULATION OF THE TEMPERATURE DEPENDENCE FOR ABSORPTION IN $CO_{2}$ IN THE 1750-1200 \AA REGION

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 Title: CALCULATION OF THE TEMPERATURE DEPENDENCE FOR ABSORPTION IN $CO_{2}$ IN THE 1750-1200 \AA REGION Creators: Julienne, P. S.; Neumann, D.; Krauss, M. Issue Date: 1971 Publisher: Ohio State University Abstract: The absorption cross section of the diffuse absorption bands of $CO_{2}$ in the region 1750-1200 \AA is of prime importance for understanding $CO_{2}$ photolysis, especially as a constituent of a planetary atmosphere. The upper state of the absorption is a $^{1}B_{2}$ state correlating with a $^{1}\Delta_{u}$ state in the linear geometry. Although the cross section for this vibronically allowed electric-dipole absorption will be temperature dependent, there are no experimental studies of this temperature dependence, and room temperature values have been used in discussions of the atmospheres of Mars and Venus despite the widely disparate temperature distributions of their atmospheres. We have calculated the temperature dependence of the integrated absorption coefficient for the 1750-1200 \AA region. The electronic energies and transition moments were calculated ab initio as a function of the bending angle of the molecule; the Renner type splitting of the degenerate $^{1}\Delta_{u}$ state into $^{1}B_{2}$ and $^{1}A_{2}$ energy curves is obtained. The integrated absorption cross section is proportional to the square of the transition moment averaged over the ground state vibrational wave functions. At room temperature the average of the transition moment squared over a Boltzmann distribution is $2.9 \times 10^{-3}$ $(ea_{{o}})^{2}$, which corresponds roughly to an oscillator strength of $6 \times 10^{-4}$. Although halving the temperature produces only about 10\% decrease in absorption, there is a dramatic increase by 75\% when the temperature is doubled. The temperature dependence of individual lines, particularly in the wings of the overall distribution, is likely to be even more sensitive. Description: Author Institution: National Bureau of Standards URI: http://hdl.handle.net/1811/8652 Other Identifiers: 1971-D-1