Mechanism for production of the Fourth Positive Band System of CO by electron impact on CO₂

The electron impact energy loss spectrum for CO2 is presented over an energy range of 10 to 20 ev. Analysis of this spectrum and molecular orbital calculations indicate that valence state perturbers of 1Σu+ and 1Πu symmetry contribute significantly to the oscillator strength in the range from 11 to 14 ev. The 1Σu+ state is then determined to be the predominant contributor to the reaction CO2 + e → CO2(1Σu+) + e → CO(A1Π) + O(3P) + e. Unusual intensity distributions in the observed fluorescence of the vibrational states of CO(A1Π) observed by M. J. Mumma, E. J. Stone, and E. C. Zipf (1970) are explained on the basis of competition between predissociation and autoionization from this single excited state. This mechanism would be one means for production of the fourth positive bands of CO in the ultraviolet dayglow of the upper atmosphere of Mars.