Inelastic squared form factors of the vibronic states of B1Σu+, C1Πu , and EF1Σg+ for molecular D2 studied by high-energy electron scattering

Abstract

The inelastic squared form factors of the valence-shell excitations of ${\mathrm{D}}_{2}$ were measured by high-energy electron scattering and calculated by the multireference single- and double-excitation configuration interaction method in the present work. It is found that for the ${B}^{1}{\mathrm{\ensuremath{\Sigma}}}_{u}{}^{+}$ state of ${\mathrm{D}}_{2}$, the theoretical calculation cannot satisfactorily reproduce the inelastic squared form factors with a higher vibrational quantum number. For the vibronic states of ${C}^{1}{\mathrm{\ensuremath{\Pi}}}_{u}$ and $E{F}^{1}{\mathrm{\ensuremath{\Sigma}}}_{g}{}^{+}$ of ${\mathrm{D}}_{2}$, obvious discrepancies between our electron-scattering results and theoretical calculations are found. Similar phenomena observed for ${\mathrm{H}}_{2}$, HD, and ${\mathrm{D}}_{2}$ may be attributed to electronic-vibrational coupling and the failure of the first Born approximation at an incident electron energy of 1500 eV. Furthermore, the present inelastic squared form factors of ${\mathrm{D}}_{2}$ are in good agreement with the ones of ${\mathrm{H}}_{2}$ and HD, which indicates that there is no isotope effect for the electronic matrix elements of ${\mathrm{H}}_{2}$, HD, and ${\mathrm{D}}_{2}$ in the momentum space.