Reconstruction of attosecond beatings by two-photon interferences (RABBIT) has amply been used to retrieve photoionization delays from photoelectron spectra measured in atoms and, more recently, in molecules. For the latter, the molecular orientation and multicenter nature of the potential felt by the escaping electron often makes the extraction of these delays problematic. One of the complications comes from the fact that the energy separation between the states of the resulting molecular cation is of the order of the photon energy of the driving infrared (IR) field, so that, during the ionization process, the IR field may induce resonant transitions between such states. This adds a third ionization path to the standard two-path ionization scheme of RABBIT. Here we present a detailed theoretical study of RABBIT in the acetylene molecule in which we have explicitly evaluated time-resolved photoelectron spectra as those recorded in actual experiments. We do so for both random and well-defined orientations of the molecule, and for photoelectron spectra integrated over and resolved in the photoelectron emission angle. We show that the presence of this additional third path can strongly affect the values and physical meaning of photoionization delays extracted from fits based on the commonly used two-path interference scheme. This is indeed the case for acetylene molecules parallel to the light polarization direction, where the extracted delays strongly depend on the IR frequency, while for molecules perpendicular to the polarization direction the standard two-path RABBIT conditions are fulfilled.

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• Atomic & molecular processes in external fields
• Electronic excitation & ionization
• Single- and few-photon ionization & excitation