Speaker
Description
Inter-molecular interactions (in particular hydrogen bonding) influence solvation and reaction pathways, and investigations of electronic structure and dynamics on the molecular level are important for a detailed understanding of chemical processes in solution.
In this presentation of a few case studies, I discuss how multi-configuration quantum chemistry (particularly RASPT2) , density functional theory (DFT) and ab initio molecular dynamics (AIMD) simulations can be used to study hydrogen bonding and excited state dynamics in solution and for simulations of X-ray spectra.
The performance of DFT methods for simulations of nitrogen K-edge X-ray absorption spectra is discussed in relation to the pH dependence in the hydrogen bond environment and electronic structure of aqueous ammonia/ammonium [1]. Furthermore, the influence of hydrogen bonding and core-excited state dynamics on resonant inelastic X-ray scattering (RIXS) is established [2].
To conclude, I will discuss our contributions to rationalize time-resolved iron L-edge and N K-edge RIXS and get insight into valence excited state dynamics in iron complexes and chromophores in solution [3]. The interpretation of L-edge spectra is complicated and relies on accurate theoretical modeling and spectrum simulations to take into account effects of multiplet effects, spin-orbit coupling, chemical interactions, dynamics in the spectroscopic process [4]. The multi-configurational restricted active space method (RASPT2) is an efficient well-targeted approach for the purpose of simulating X-ray spectra, in particular for following distorted geometries along chemical pathways.
[1] M. Ekimova, W. Quevedo, Ł. Szyc, M. Iannuzzi, Ph. Wernet, M. Odelius, and E. T. J. Nibbering. Aqueous solvation of ammonia and ammonium: Probing hydrogen bond motifs with FT-IR and soft-x-ray spectroscopy. J. Am. Chem. Soc., 139:12773–12783 (2017).
[2] L. Weinhardt, E. Ertan, M. Iannuzzi, M. Weigand, O. Fuchs, M. Bär, M. Blum, J. D. Denlinger, W. Yang, M. Odelius E. Umbach, and C. Heske. Probing hydrogen bonding orbitals: resonant inelastic soft x-ray scattering of aqueous NH3. Phys. Chem. Chem. Phys., 17:27145–27153, (2015).
[3] Ph. Wernet, K. Kunnus, I. Josefsson, I. Rajkovic, W. Quevedo, M. Beye, S. Schreck, S. Grübel, M. Scholz, D. Nordlund, W. Zhang, R. W. Hartsock, W. F. Schlotter, J. J. Turner, B. Kennedy, F. Hennies, F. M. F. de Groot, K. J. Gaffney, S. Techert, M. Odelius, and A. Föhlisch. Orbital-specific mapping of the ligand exchange dynamics of Fe(CO)5 in solution. Nature, 520:78–81 (2015).
[4] I. Josefsson, K. Kunnus, S. Schreck, A. Föhlisch, F. de Groot, Ph. Wernet, and M. Odelius. Ab initio calculations of x-ray spectra: Atomic multiplet and molecular orbital effects in a multi-configurational scf approach to the L-edge spectra of transition metal complexes. J. Phys. Chem. Lett., 3:3565–3570 (2012).
