Generalized oscillator strengths for the vibronic bands of ${\mathrm{A}}^1$Π, ${\mathrm{B}}^1$${\mathrm{\Sigma }}^{+}$, ${\mathrm{C}}^1$${\mathrm{\Sigma }}^{+}$, and ${\mathrm{E}}^1$Π have been determined by an angle-resolved electron energy loss spectroscopy at an incident electron energy of 1500 eV and in an angular range of 0.5°–6.0°. The corresponding absolute optical oscillator strengths obtained by extrapolating the generalized oscillator strengths to ${\mathrm{K}}^2$=0 are also reported. The present results have been compared with previous work, and some differences between them have been explained. The experimental generalized oscillator strengths for ${\mathrm{v}}^{|\mathrm{I}\mathrm{H}}$=0–8 of ${\mathrm{A}}^1$Π, ${\mathrm{v}}^{|\mathrm{I}\mathrm{H}}$=0–1 of ${\mathrm{B}}^1$${\mathrm{\Sigma }}^{+}$, ${\mathrm{C}}^1$${\mathrm{\Sigma }}^{+}$, and ${\mathrm{E}}^1$Π are reported.

DOI:https://doi.org/10.1103/PhysRevA.55.1799