Where to Find ICEC? – Screening 2442 Systems for Interparticle Coulombic Electron Capture

Interparticle Coulombic Electron Capture (ICEC) is an environment-assisted process where an electron is captured by an acceptor, and the resulting excess energy is transferred to a donor, which subsequently ionizes. To identify systems where this process is efficient enough to compete with photorecombination, the authors conducted a large-scale computational screen of 2442 atom-atom and atom-molecule combinations. They employed an efficient asymptotic approximation, which allows for the calculation of cross sections based on the properties of isolated units. While interparticle nuclear dynamics were neglected to facilitate this extensive survey, the researchers incorporated intramolecular nuclear motion for molecular donors using a Franck-Condon model.

The screening identified several classes of systems with high ICEC efficiency. Notable candidates include halogen-halide systems and combinations involving a proton and diatomic molecules like N2, O2, CO, and NO. The study highlights that the ICEC cross section generally decreases with the fourth power of the transferred energy, but is significantly modulated by the electronic and vibrational structure of the participating units. For instance, the authors observed that electronic channel openings in the donor can increase the ICEC cross section, while vibrational resonances in molecular donors—such as those seen in H+O2—can lead to distinct peaks in the cross-section profile. Additionally, the presence of Cooper minima in the photoionization cross sections of certain atoms can cause sharp, characteristic dips in the ICEC cross section.

ICEC is a critical mechanism for electron attachment in environments where isolated photorecombination is inefficient. By providing a systematic ranking of 2442 systems, this work serves as a roadmap for experimentalists to target specific, high-probability candidates for laboratory verification. The identification of atmospheric and astrochemical species as promising ICEC candidates suggests that this process may play a previously underappreciated role in the chemical evolution of these environments.