The low-energy electron-scattering resonances of pyrene were characterized using experimental and computational methods. Experimentally, a two-dimensional photoelectron imaging of the pyrene anion was used to probe the dynamics of resonances over the first 4 eV of the continuum. Computationally, the energies and character of the anion states were determined using equation-of-motion coupled cluster calculations, while taking specific care to avoid the collapse onto discretized continuum levels, and an application of the pairing theorem. Our results are in good agreement with the predictions of electron-scattering calculations that include an offset and with the pyrene anion absorption spectrum in a glass matrix. Taken together, we offer an assignment of the first five electronic resonances of pyrene. Some of the population in the lowest-energy 2B1u resonance was observed to decay to the ground electronic state of the anion, while all other resonances decay by a direct autodetachment. The astronomical relevance of a ground-state electron capture proceeding via a low-energy resonance in pyrene is discussed.

The stabilization method is widely used to theoretically characterize temporary anions and other systems displaying resonances. In this approach, information about a metastable state is encoded in the interaction of a diabatic discrete state and discretized continuum solutions, the energy of which are varied by scaling the extent of the basis set. In this work, we identify the aspects of the coupling between the discrete state and the discretized continuum states that encode information about the existence of complex stationary points and, hence, complex resonance energies in stabilization graphs. This allows us to design a simple two-level model for extracting complex resonance energies from stabilization graphs. The resulting model is applied to the 2Πg anion state of N2.

In this work, it is demonstrated that a simple analytical expression, (A/R 2) exp false( prefix− B / μ − μ cr false) , where μ is the dipole moment, μcr is the critical dipole moment, and A and B are constants, accurately describes the binding energy of an electron in the field of a finite fixed dipole over a wide range of dipole moments. It is also demonstrated that this expression provides an accurate fit to the experimental electron binding energies for the dipole-bound anions of a series of phenoxy radicals. A simple extension of this expression is found to be applicable when the dipole model is extended to include short-range repulsion and polarization interactions.

In a diabatic picture metastable states subject to decay by electron detachment can be viewed as arising from the coupling between a discrete state and a continuum. In treating such states with bound-state quantum chemical methods, the continuum is discretized. In this study, we elucidate the role of overlap in this interaction in the application of the stabilization method to temporary anion states. This is accomplished by use of a minimalist stabilization calculation on the lowest energy = 2 (D) resonance of the finite spherical well potential using two basis functions, one describing the diabatic discrete state and the other a diabatic discretized continuum state. We show that even such a simple treatment predicts a complex resonance energy in good agreement with the exact result. If the energy of the discrete state is assumed to be constant, which is tantamount to orthogonalizing the discretized continuum state to the discrete state, it is demonstrated that the square of the off-diagonal coupling has a maximum close to the crossing point of the orthogonalized diabatic curves and that the curvature in the coupling is responsible for the complex stationary point associated with the resonance. Moreover, this curvature is a consequence of the overlap between the two diabatic states.