Single-photon ionization of the HeH${}^{2+}$ molecular ion exposed to an attosecond x-ray laser pulse is investigated for photon energies of 200 and 300 eV. In the fixed-nuclei approximation, the temporal response of the system is obtained by solving the time-dependent Schrödinger equation through an ab initio time-dependent grid-based discrete-variable representation formulated in two-center prolate spheroidal coordinates. The two-center interference effect is clearly observable in the excited $2p\sigma$ state, whereas interference patterns almost disappear, in both the parallel and perpendicular geometries, when the system is started from the $1s\sigma$ ground state. The angular distributions are asymmetric with respect to the center between the helium and hydrogen nuclei. For the $2p\sigma$ state in the parallel geometry, a dynamically forbidden mode of photoionization is observed only on one side of the two nuclei, with the details depending on the laser parameters and the internuclear separation. We also address the similarities and differences between a plane-wave model for the ejected electron with a linear combination of atomic orbitals for the molecular bound states and the classical double-slit-like interference pattern.

• Received 24 September 2012

DOI:https://doi.org/10.1103/PhysRevA.86.053425