Isotope Effects in Molecular Scattering by Electrons

Recent improvement in electron-beam resolution has made possible the direct study of isotope effects in differential cross sections in ${\mathrm{H}}_2$ and ${\mathrm{D}}_2$. The observation of the reduced-mass dependence (${\mu }^{-\frac{1}{2}}$) of vibrational ($v=0\mathrm{}\to 1$) cross sections and isotopic independence of rotational cross sections at 4 eV has been understood using the frame-transformation theory. Generalization and limitation of the theory are discussed. Specific predictions are made for cross sections in HD, HT, DT, and ${\mathrm{T}}_2$.