Modeling the N2 Lyman-Birge-Hopfield bands in the dayglow:: Including radiative and collisional cascading between the singlet states

A new model for the daytime airglow emissions from the Na Lyman-Birge-Hopfield (LBH) bands (a(1)II(g)-X(1)Sigma(g)(+)) in the Earth's atmosphere is presented. This model gives good agreement, which other first principles models have been unable to obtain, with dayglow observations reporting increased vibrational populations, relative to direct excitation, for v less than or equal to 1 of the N-2 a(1)II(g) state. The ability of the model to match the observations is due to the inclusion of radiative and collisional cascading between the singlet states. Such cascading was not included in previous first principles dayglow calculations for the singlet states. Not only does cascading improve the fit between the observed and modeled relative vibrational populations, it also increases the total emission from the LBH bands by a factor of similar to 1.6 due to the transfer of excitation from the a' and w states to the a state, resulting in significantly greater emission than predicted by earlier models using the same excitation cross section for the a state. Such an increase in the total emission from the LBH bands is consistent with recent work by Budzien et al. [1994] and Link et al. [1994]. The coupling between the singlet states will have a significant impact on the interpretation of the LBH band emissions from the Earth's atmosphere.