Theory of nonradiative decay with two or more electrons at play

UNBOUND TWO aims to develop the quantum chemistry methods that are needed to interpret next-generation spectroscopy involving two or more unbound electrons and to understand chemical reactions involving unbound doubly-excited states. Emerging spectroscopies can probe correlations between two electrons, which is fundamentally impossible with techniques that probe only one electron. To gain information about electronic and molecular structure from such spectra, theoretical modeling is key. However, existing methods are able to deal with only one emitted electron or they are geared toward atoms. As a result, the full potential of spectroscopy is not yet realized for molecules.Electron attachment accompanied by electronic excitation can mediate unique chemical reactions that attachment to the ground state does not support, for example the cleavage of OH bonds. Theoretical modeling is essential to harness such reactions, but existing methods struggle with the pivotal unbound doubly-excited states so that electron-induced chemistry is still at an early stage.Building on recent breakthroughs for nonradiative decay in which only one electron becomes unbound, we will investigate processes in which two or more electrons are at play, for example in Auger and Coster-Kronig cascades and in dissociative electron attachment and dissociative recombination. To achieve these goals, we will advance the quantum chemistry of unbound electrons substantially. We will develop methods that treat singly-excited and doubly-excited states evenhandedly and describe the correlated motion of two emitted electrons. In computational applications, we will study the interaction of organic molecules and transition-metal compounds in gas phase and solution with ionizing radiation and free electrons over an energy range from <0.1 to >1000 eV.