Investigation of Nuclear Hyperfine Coupling in H2 Heterodimers Using Rotational Spectroscopy

by Robin Maria Magdalena Dohmen
Doctoral thesis
Date of Examination:2024-06-26
Date of issue:2025-05-20
Advisor:Prof. Dr. Daniel Obenchain
Referee:Prof. Dr. Daniel Obenchain
Referee:Prof. Dr. Martin Suhm
Referee:Prof. Dr. Marina Bennati
Referee:Prof. Dr. Konrad Koszinowski
Referee:Prof. Dr. Nadja A. Simeth
Referee:PD Dr. Oliver Bünermann
Referee:Dr. Tim Schäfer
Persistent Address: http://dx.doi.org/10.53846/goediss-11273

 

 

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Abstract

English

Rotational spectroscopy of gas phase compounds is a powerful technique for structure determination through the unique moments of inertia of a molecular system. It is sensitive angular momentum coupling; therefore, complicated splitting patterns caused by nuclear hyperfine coupling commonly arise in rotational spectra. Electronic nuclear quadrupole coupling is highly sensitive to the electronic environment and acts as a spectroscopic probe to complement structure determination. Dipolar spin coupling is dependent on the distance between the coupling spins; thus, both parameters are useful for structural investigations. In this thesis, electronic and magnetic nuclear spin couplings were investigated for structural analysis of hydrogen complexes with storage molecule mimics through rotational spectroscopy. This involved theoretical benchmarking of electronic nuclear quadrupole coupling in molecular complexes and experimental determination of nuclear quadrupole coupling constants hydrogen storage molecular mimics, a series of chlorobenzaldehyde isomers. The experiments revealed errors in the theoretical description of the quadrupole coupling constants introduced by the projection into the principal axis system for the near-oblate 2-chororbenzaldehyde isomer. Moving to hydrogen, five different organic molecules were investigated as dispersive binding partners for hydrogen. In each complex, the hydrogen interacted exclusively with the aromatic ring system. A separate treatment of the hydrogen nuclear spin states was performed and a novel conjoint fit of both spin states, treating ortho hydrogen as an internal rotor, was successfully applied. The structure of the hydrogen complexes was investigated with three different approaches, including the structural information contained in the magnetic nuclear spin coupling of the ortho hydrogen complex. The hydrogen complexes presented in this thesis are the first detection of hydrogen’s dispersive interactions with aromatic rings through rotational spectroscopy. It provides a stepping stone for further research of hydrogen complexes with heavier binding partners and the treatment of the hydrogen angular momentum in the rotational Hamiltonian.
Keywords: Physical Chemistry; Structure determination; Rotational Spectroscopy; Benchmarking; Nuclear Quadrupole Coupling; Hydrogen
 
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