Angle-resolved (e, e+ion) spectroscopy: stereodynamics in electron impact ionization of molecules

Electron energy loss spectroscopy (EELS) has proven to be a powerful tool for the study of electronic structures and excitation dynamics of atoms and molecules. The momentum transfer dependence of the electron scattering cross section provides a wealth of information about the excited electronic states and gives deep insight into the nature of the excitation processes of interest. However, EELS studies on molecules have long been limited to the investigation of targets with random spatial orientation; spherical averaging over the molecular orientation results in an enormous loss of information. To overcome this difficulty, we have developed an electron-ion coincidence apparatus [1]. The orientation of the target molecule at the moment of electron collision can be determined from the recoil direction of the fragment ion. Using this (e, e+ion) technique, we have shown that the molecular orientation dependence of autoionization reflects the spatial shape of the excited molecular orbital [2], and have also revealed the role of molecular symmetry in the dissociative ionization [3] and the effects of non-dipole interactions on shape resonance [4].

[1] N. Watanabe et al., Rev. Sci. Instrum. 89, 043105 (2018).

[2] N. Watanabe et al., Phys. Rev. A 95, 060702(R) (2017); 99, 022704 (2019).

[3] N. Watanabe and M. Takahashi, J. Chem. Phys. 152, 164301 (2020); Phys. Rev. A 104, 032812 (2021).

[4] N. Watanabe and M. Takahashi, Phys. Rev. A 108, 042814 (2023).