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Setting the stage for theoretical X-ray spectra of the H2S molecule with RASPT2 calculations of the energy landscape
Stockholm University, Faculty of Science, Department of Physics.ORCID iD: 0000-0002-4603-2097
Stockholm University, Faculty of Science, Department of Physics.ORCID iD: 0000-0002-7023-2486
(English)Manuscript (preprint) (Other academic)
Abstract [en]

Electronic valence- and core-excitations into the anti-bonding orbitals of the H2S molecule have been calculated within a multi-configurational wave-function framework (RASPT2). Potential energy surfaces and transition dipole moments have been derived in two dimensions for the S-H stretching coordinates. The |S1s-1, 6a11> and |S1s-1, 3b21> core-excited states in H2S are nearly degenerate along the symmetric stretching coordinate, for which we have identified two conical intersections. The small energy splitting of the S1s-1 core-excited states at equilibrium geometry arise from an avoided crossing at broken symmetry. Compared to the water molecule, which exhibit state-selective gating to different vibrational modes [Nat. Commun. 8 14165 (2017)] in its well-separated O1s-1 core-excited states, we expect a strong coupling between the close-lying |S1s-1, 6a11> and |S1s-1, 3b21> states. This could lead to dissociative dynamics observable in K-edge RIXS. The S2p-1 core-excited states form two dense manifolds of spin-orbit coupled states, which can be schematically characterised as bound |S2p-1,3b21> and dissociative |S2p-1,6a11> states. We identify three conical intersections in the singlet and triplet states along the symmetric stretching coordinate. Mapping the molecular singlet and triplet states to the atomic dissociation limit reveals a symmetry selection rule, leading to an off-set of the 1|3a1-1,6a11> state relative to the other S2p-1 core-excited states. The dense manifolds of S2p-1 core-excited states will complicate the analysis of Kα-edge RIXS, but dynamical effects could be evaluated through detuning and in comparison to L-edge XAS. In L-edge RIXS, the dynamical effects well be more pronounced due to a longer life-time of the S2p-1 core-excited states compared to the S1s-1 core-excited states.

National Category
Atom and Molecular Physics and Optics
Research subject
Chemical Physics
Identifiers
URN: urn:nbn:se:su:diva-154021OAI: oai:DiVA.org:su-154021DiVA, id: diva2:1189857
Available from: 2018-03-13 Created: 2018-03-13 Last updated: 2018-03-20Bibliographically approved
In thesis
1. Quantum chemical calculations of multidimensional dynamics probed in resonant inelastic X-ray scattering
Open this publication in new window or tab >>Quantum chemical calculations of multidimensional dynamics probed in resonant inelastic X-ray scattering
2018 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

This thesis is devoted to the theoretical study of the dynamical processes induced by light-matter interactions in molecules and molecular systems. To this end, the multidimensional nuclear dynamics probed in resonant inelastic X-ray scattering (RIXS) of small molecules, exemplified by H2O (g) and H2S (g), as well as more complex molecular systems, exemplified by NH3 (aq) and kaolinite clay, are modelled. The computational methodology consists of a combination of ab initio quantum chemistry calculations, quantum nuclear wave packet dynamics and in certain cases molecular dynamics modelling. This approach is used to simulate K-edge RIXS spectra and the theoretical results are evaluated against experimental measurements.

Specifically, the vibrational profile for decay back to the electronic ground state of the H2O molecule displays a vibrational selectivity introduced by the dynamics in the core-excited state. Simulation of the inelastic decay channel to the electronic |1b1-1,4a11> valence-excited state shows that the splitting of the spectral profile arises from the contribution of decay in the OH fragment. The character of the S1s-1 and S2p-1 core-excited states of the H2S molecule has been investigated and distinct similarities and differences with the H2O molecule have been identified. RIXS has also been used as a probe of the hydrogen bonding environment in aqueous ammonia and by detailed analysis of the valence orbitals of NH3 and water, the spectral profiles are explained. Finally, it is shown that vibrations of weakly hydrogen bonding OH are excited in RIXS decay to the electronic ground state in kaolinite. 

Place, publisher, year, edition, pages
Stockholm: Department of Physics, Stockholm University, 2018. p. 82
Keyword
quantum chemistry, X-ray spectroscopy, RASSCF, density functional theory, ultrafast nuclear dynamics
National Category
Atom and Molecular Physics and Optics
Research subject
Chemical Physics
Identifiers
urn:nbn:se:su:diva-154057 (URN)978-91-7797-173-3 (ISBN)978-91-7797-174-0 (ISBN)
Public defence
2018-05-04, sal FP41, hus 1, AlbaNova universitetscentrum, Roslagstullsbacken 21, Stockholm, 13:00 (English)
Opponent
Supervisors
Note

At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 3: Manuscript. Paper 4: Manuscript.

Available from: 2018-04-11 Created: 2018-03-15 Last updated: 2018-04-04Bibliographically approved

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