Resonances in low-energy electron scattering from <i>para</i>-benzoquinone

We present detailed ab initio scattering calculations for electron collisions with para-benzoquinone. The R-matrix method has been used to study elastic and electronically inelastic scattering. We have identified 25 resonances of shape, Feshbach, core-excited shape and mixed character between 0 and 8 eV. Agreement of our resonance spectrum with existing literature is discussed, in particular that of the low-lying resonances that participate in the photodetachment process. Integral elastic and total inelastic cross sections are also presented

Resonances in molecules and molecular clusters

Resonances play an important role in a number of atomic and molecular processes. Identifying and characterising resonances in electron scattering is essential as they can both enhance a number of processes (e.g. electronic and vibrational excitation) and are crucial in others like dissociative electron attachment and dissociative recombination. We discuss recent theoretical studies of shape and core-excited resonances, both in isolated molecules of biological relevance and in small molecular clusters. The latter are investigated to understand the effect of the environment, in particular hydration, in electron collisions in biological matter

Theoretical study of resonance formation in microhydrated molecules. I. Pyridine-(H₂O)_n, n = 1,2,3,5

We present R-matrix calculations for electron scattering from microhydrated pyridine. We studied the pyridine-H2O cluster at static-exchange (SE), SE + polarization, and close-coupling levels, and pyridine-(H2O)n n = 2, 3, and 5 at SE level only in order to investigate the effect of hydrogen bonding on the resonances of pyridine. We analyse the results in terms of direct and indirect effects. We observe that the total (direct plus indirect) effect of microhydration leads to the stabilization of all resonances studied, both shape and core-excited. The size of the shift is different for different resonances and seems to be linked to the dipole moment of the cluster

Shape and core-excited resonances in electron scattering from alanine

We present detailed ab initio scattering calculations using the R-matrix method for electron collisions with the most stable conformer of α-alanine. The shape resonances that we identify are in good agreement with earlier calculations and experiments. Core-excited and mixed-character resonances are identified and characterized computationally for the first time. Dissociative electron attachment results are discussed in relation to the resonances identified

reskit: a toolkit to determine the poles of an S-matrix

We present the python package reskit, developed to calculate the coefficients of an analytical continuation of the S-matrix of a physical system by means of Padé approximants and, from this fit, determine the complex poles of this S-matrix. The current implementation of the program is restricted to elastic scattering, i.e. cases in which all channels have the same energy. It has been tested using as input ab initio scattering data for electron-molecule collisions obtained for energies along the real axis. The identification and characterisation of the resonances present in the systems using reskit is described and discussed

Interatomic Coulombic electron capture from first principles

Interatomic Coulombic electron capture (ICEC) is an environment-assisted process in which a free electron can efficiently attach to an ion, atom or molecule by transferring the excess energy to a neighboring species. Absolute cross sections are necessary to evaluate the relative importance of this process. In this work, we employ the R-matrix method to compute ab initio these cross sections for a singly charged neon ion embedded in small helium clusters. Our results show that the ICEC cross sections are several orders of magnitude higher than anticipated and dominate other competing processes. Electron energy loss spectra on an absolute scale are provided for the Ne+@He20 cluster. Such spectra exhibit an unambiguous signature of the ICEC process. The finding is expected to stimulate experimental observations

Elastic and inelastic low-energy electron collisions with pyrazine

We present results of ab-initio scattering calculations for electron collisions with pyrazine using the R-matrix method, carried out at various levels of approximation. We confirm the existing experimental and theoretical understanding of the three well-known Π* shape resonances. In addition, we find numerous core-excited resonances (above 4.8 eV) and identify their most likely parent states. We also present differential cross sections, showing high sensitivity to the scattering model chosen at low energies. We make recommendations regarding the selection of models for scattering calculations with this type of targets

Shape and Core-Excited Resonances in Thiophene

We present a comprehensive study of resonance formation in electron collisions with thiophene. Detailed calculations have been performed using the ab initio R-matrix method. Three shape resonances previously described, two of π* character and one σ*, as well as a number of resonances of core-excited or mixed character are identified and characterized. Differential cross sections for electron impact excitation up to 18~eV and for two scattering angles, 90° and 135°, are measured. The measured cross sections provide experimental confirmation for a number of the core-excited resonances. The link between these resonances and prior DEA experiments is discusse