Conical intersections induced by classical and quantum light

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Free polyatomic molecules abundantly exhibit conical intersections (CIs) between their potential energy surfaces. Following electronic excitation (or ionization), these CIs have a substantial impact on the ensuing nuclear dynamics leading to strong non-adiabatic effects. CIs can also be induced by classical (laser) and quantum (cavity) light and this even in diatomic molecules. The impact of these two kinds of light-induced CIs (LICIs) has only very little been explored for polyatomic molecules. This project addresses two main issues. a) Ionization in the presence of a quantum field which couples resonantly ionic states. The molecule chosen (butatriene) is known to have a natural CI which strongly affects the ionization spectrum of the free molecule. The investigation of the interplay between the natural CI and the LICI stands in the center of this subproject. For comparison, the spectrum with a LICI induced by a laser field will also be computed and studied. b) Probing non-adiabatic dynamics in a cavity after exciting the molecule by a classical field. The polaritonic states formed are hybrid photonic-electronic states and the cavity can radiate during the nuclear dynamics. The main point is to study the dynamics and, in addition, explore whether there is a relationship between the non-adiabatic dynamics and the radiation which is measureable. Two cases will be studied, one (formaldehyde) where there is no natural CI involved, and one (pyrazine) where a natural CI is present and we can investigate the interplay with the LICI. Since the project is on new fundamental effects, the systems to be studied were chosen such that they are sufficiently complex to validate the phenomena and sufficiently known to allow for accurate calculations needed for future predictions.