Theory of rotational branch structure with application to N2 and CO

Analysis of rotational branch structure in high resolution electron energy-loss spectroscopy is greatly facilitated by a high j approximation to the Clebsch-Gordan coefficient. A more accurate approximation than Read's is found for molecules in the Sigma state. When assimilated into the theory of Chang, the resulting expressions for the branch differential cross sections for N2 and CO turn out to be easily evaluated by hand. In both cases, good agreement is found with experiment in both the shape and the magnitude of the cross sections at an electron energy of around 2 eV.