Two-center interference in H2+ photoionization by electric dipole and quadrupole transitions

In molecular photoionization, the two-center interference is widely described within the electric dipole approximation, neglecting the electric quadrupole effect. By numerically solving the two-dimensional time-dependent Schr\"odinger equation beyond the dipole approximation and using perturbation theory, we demonstrate that the two-center interference structure induced by the electric quadrupole transition in the one-photon ionization of H₂⁺ can be observed in the asymmetric photoelectron yield along the laser propagation direction. Compared with the dipole transition, the electron wave packets emitted from the two nuclei of the molecule due to the electric quadrupole transition exhibit an additional phase difference. This phase difference results in a distinct two-center interference structure compared to the dipole transition. Furthermore, an experimental scheme based on the reconstruction of attosecond beating by interference of two-photon transitions is proposed to reveal the two-center interference structure induced by the electric quadrupole transition. Our study provides a different perspective for investigating the nondipole effect in molecular photoionization.