We use the adiabatic-nuclei molecular convergent close-coupling method to perform calculations of 0.01–1000 eV electrons scattering on the $c{}^3\mathrm{\Pi }_u$, $a{}^3\mathrm{\Sigma }_g^{+}$, $B{}^1\mathrm{\Sigma }_u^{+}$, $C{}^1\mathrm{\Pi }_u$, and $EF{}^1\mathrm{\Sigma }_g^{+}$ states of ${\mathrm{H}}_2$ in the $v=0$ vibrational level. Elastic, superelastic, ionization, and grand-total cross sections are presented, as well as cross sections for excitation of the $n=2$–3 singlet and triplet states of ${\mathrm{H}}_2$ (where $n$ is the atomic-limit principle quantum number). Comparison with available theoretical results is made. Good agreement is found with the recent $R$-matrix results [ J. Phys. B 53, 245203 (2020)] for most of the exchange and dipole-forbidden transitions, but not for the dipole-allowed transitions. The sources of disagreement were found to be an unconverged partial-wave expansion and the utilization of the fixed-nuclei approximation (as opposed to adiabatic-nuclei) in the $R$-matrix calculations.

We describe astra (attosecond transitions), a close-coupling approach to molecular ionization that uses many-body transition-density matrices between ionic states with arbitrary spin and symmetry, in combination with hybrid integrals between Gaussian and numerical orbitals, to efficiently evaluate photoionization observables. Within the transition-density-matrix approach, the evaluation of interchannel coupling is exact and does not depend on the size of the configuration-interaction space of the ions. Thanks to these two crucial features, astra opens the way to studying highly correlated and comparatively large targets at a manageable computational cost. Here, astra is used to predict the parameters of bound and autoionizing states of the boron atom and of the ${\mathrm{N}}_2$ molecule, as well as the total photoionization cross section of boron, the nitrogen molecule $\left({\mathrm{N}}_2\right)$, and formaldehyde $\left({\mathrm{H}}_2\mathrm{CO}\right)$. Our results are in excellent agreement with theoretical and experimental values from the literature.