A detailed study of the vibrational states of CO2 in the upper atmosphere was conducted in order to enable the calculation of emission near 2.7 &mgr;m expected for sunlit conditions. New line-by-line computer codes were used to evaluate the solar pumping of vibrational levels and to calculate the limb radiance. Excitation and quenching mechanisms are quantified and compared for several important vibrational states in the altitude range 40-110 km. The dominance of fluorescent CO2 hot band emission for altitudes below 75 km is confirmed. The spectral distribution, and to a lesser degree the total band radiance, are shown to be very sensitive to collisional interactions. Detailed results are presented and compared with experiment.