Understanding electronic excitation and multi-photon ionization spectra, particularly those involving strongly correlated states or those involving larger molecules with transition metal centers, poses a significant challenge for theory and experiment. The existing experimental techniques may not be sufficiently powerful to provide definitive information on their own, whereas an accurate treatment of the relevant many-electron correlation effects required in theoretical analyses may be far from obvious. This talk will highlight the transformative role that theory has played in understanding two sets of experiments. The first example deals with the discovery of the doubly excited state of azulene, located below the ionization threshold and mediating the 1+2' multi-photon ionization that leads to a Rydberg fingerprint, using novel electronic structure methods based on the equation-of-motion coupled-cluster (EOMCC) theory. The second example focuses on the nature of the low-lying excited states of methylcobalamin, where conventional methods based on density functional theory (DFT) support any of the existing and conflicting interpretations of the S0?S1 electronic transition and where high-level ab initio calculations employing the EOMCC and multi-reference perturbation theories provide definitive answers.

Understanding photochemistry and photo-ionization dynamics with highly correlated electronic structure methods: Two examples that highlight the transformative role of theory in the interpretation of experimental observations

247th National Meeting (2014)

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