We theoretically explore a variant of RABBITT spectroscopy in which the attosecond-pulse train comprises isolated pairs of consecutive harmonics of the fundamental infrared probe frequency. In this scheme, one-photon and two-photon amplitudes interfere resulting in an asymmetric photoelectron emission. This interferometric principle has the potential of giving access to the time-resolved ionization of systems that exhibit autoionizing states, since it imprints the group delay of both one-photon and two-photon resonant transitions in the energy-resolved photoelectron anisotropy as a function of the pump-probe time delay. To bring to the fore the connection between the pump-probe ionization process and its perturbative analysis, on the the one side, and the underlying field-free scattering observables as well as the radiative couplings in the target system, on the other side, we test this scheme with an exactly solvable analytical one-dimensional model that supports both bound states and shape-resonances. The asymmetric photoelectron emission near a resonance is computed using perturbation theory as well as solving the time-dependent Schodinger equation; the results are in excellent agreement with the field-free resonant scattering properties of the model.
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