Setting the stage for theoretical x-ray spectra of the H2S molecule with multi-configurational quantum chemical calculations of the energy landscape

Emelie Ertan; Marcus Lundberg; Lasse Kragh Sørensen; Michael Odelius

doi:10.1063/1.5145139

Setting the stage for theoretical x-ray spectra of the H₂S molecule with multi-configurational quantum chemical calculations of the energy landscape

J Chem Phys. 2020 Mar 7;152(9):094305. doi: 10.1063/1.5145139.

Authors

Emelie Ertan¹, Marcus Lundberg², Lasse Kragh Sørensen², Michael Odelius¹

Affiliations

¹ Department of Physics, Stockholm University, AlbaNova University Center, SE-106 91 Stockholm, Sweden.
² Department of Chemistry - Ångström Laboratory, Uppsala University, SE-751 20 Uppsala, Sweden.

PMID: 33480721
DOI: 10.1063/1.5145139

Abstract

In the H₂S molecule, the interplay between different core levels can be investigated in great detail in relation to x-ray spectroscopy, which requires a theory for interpretation. Hence, valence and core excitations into the two antibonding molecular orbitals of the H₂S molecule have been calculated within a multi-configurational wave function framework. Scanning along the S-H stretching coordinates, we derive potential energy surfaces and transition dipole moments involving the ground state and core and valence excited states. Both valence excitations and the S1s^-1 and S2p^-1 core excitations show pairs of dissociative and bound electronic states. These pairs of states are nearly degenerate in H₂S at the ground state geometry. The close degeneracy together with conical intersections makes H₂S an interesting target for x-ray spectroscopy involving ultra-fast dissociation influenced by non-adiabatic transitions and interference. For future investigations with x-ray absorption spectroscopy (XAS) and resonant inelastic x-ray scattering (RIXS), it is valuable to compare H₂S with the water molecule, which exhibits state-selective gating to different vibrational modes [R. C. Couto et al., Nat. Commun. 8, 14165 (2017)] in its well-separated O1s^-1 core excited states. The dense manifolds of the S2p^-1 core excited states will complicate the analysis of K_α edge RIXS, but dynamical effects could be evaluated through detuning and by comparing with L edge XAS. In L edge RIXS, the dynamical effects will be more pronounced due to the longer lifetime of the S2p^-1 core excited states compared to the S1s^-1 core excited states.