This paper investigates shape resonances in the electron-impact ionization of ${\mathrm{CF}}_4$. To this end, scattered-electron–fragment-ion coincidence experiments have been conducted for the molecule, employing an incident electron energy of 1.4 keV and a range of scattering angles from $2.2^{\circ }$ to $6.8^{\circ }$. The ionization spectra of the $C{}^{2}T_2$ ${\left(3t_2\right)}^{-1}$ and $D{}^{2}A_1$ ${\left(4a_1\right)}^{-1}$ channels have been constructed from the scattered-electron–${\mathrm{CF}}_2{}^{+}$-ion coincidence signals obtained. A resonance band at electron energy loss of $E\sim 24\mathrm{eV}$ in the $C{}^{2}T_2$ ionization channel is found to exhibit momentum-transfer dependence characteristic of a dipole-allowed transition and is attributed to the $3t_2\to \varepsilon t_2$ excitation. The spectra of the ionization to the $D{}^{2}A_1$ state manifest a broad peak centered at $E\sim 27\mathrm{eV}$, and its momentum-transfer dependence indicates that this newly identified band arises from a transition to a dipole-forbidden resonance level. The present study demonstrates that angle-resolved $(e,$ $e+\mathrm{ion})$ spectroscopy is a powerful means to investigate shape resonances in the nondipole ionization of molecules, and the outcomes provide a foundation for elucidating the impact of resonance transitions on molecular processes induced by electron impact.

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• Electron & positron scattering
• Electronic excitation & ionization
• Molecular dissociation