Doppler widths in electron quasielastic scattering from molecular gases

Recent quasielastic electron scattering experiments on some molecular gases at Ee ≥ 1.8 keV have shown that the scattering is from single isotopes of the atomic components of the gas. The scattered electron lines at definite angles are Doppler broadened by the instantaneous kinetic energy (KE) of the scattering atoms. We calculated the KE of the scattering atoms by accounting for translation, rotation, and all normal modes of vibrations of the molecule. The results reveal some large and fundamental differences from literature estimates.