Communication: Existence of the doubly excited state that mediates the photoionization of azulene

We use the high-level electronic structure computations based on the equation-of-motion coupled-cluster (EOMCC) theory to show that the previously postulated [V. Blanchet et al., J. Chem. Phys. 128, 164318 (2008)] doubly excited state of azulene, located below the ionization threshold and mediating the 1 + 2' multi-photon ionization that leads to a Rydberg fingerprint, exists. This supports the crucial role of doubly excited states in the Rydberg fingerprint spectroscopy, while demonstrating the usefulness of EOMCC methods in capturing such states.