ASTRA, a new close-coupling approach for single and double time-resolved molecular photoionization

Correlated electronic motion is at the core of light-induced chemical transformations. Until recently, attosecond science, which has opened the time-resolved study of electron dynamics, has focused on processes in which only a single extreme-ultraviolet (XUV) photon is absorbed and a single electron is liberated. New x-ray sources together with XUV-pump XUV/soft-x-ray-probe schemes promise drastically higher time resolutions. Soft-x-ray probes can excite localized core electrons, giving rise to new phenomena such as intramolecular photoelectron scattering and multiple photoionization. The theoretical description of these processes resolved in time will be  key to track the motion of correlated electron pairs. Here we present a new approach to the time-dependent close-coupling scheme for single and double multichannel molecular photoionization and an implementation of the single ionization in the new ASTRA (AttoSecond TRAnsitions) code. ASTRA structural algorithms are based on established hybrid gaussian-numerical bases and on higher-order transition density matrices (TDM) between arbitrary-spin excited ionic states of the target molecule. The TDMs are computed using a general-active-space formalism, and can treat ionic states obtained from large-scale CI calculations. Preliminary results will be presented for the N2 molecule, together with comparison with CI-singles benchmarks.