Spectroscopy of core-excited molecules and exploration of the induced dynamics

Abstract

This thesis investigates core excited electronic states of molecules in gas phase. In particular, the resonant
transitions of ionised molecules, the site-selectivity surrounding Auger-Meitner decay, and the nuclear dynamics
that may follow core excitation and ionisation.

Background: Fundamental understanding of molecules and ions lay the groundwork for all future applicative
science and production. For example, explicit understanding of dissociative mechanisms leads to control of chemical reactions.

Aims: 1) To investigate molecular states after core photoexcitation in both molecules and ions. 2) To examine
how the excited states decay through Auger-Meitner electron emission and how site-selectivity can be used to
affect the decay rate. 3) To study the various nuclear geometrical changes (isomerisation, fragmentation or bond
elongation) for the excited/ionised states.

Methods: All the experiments done for this work utilised synchrotron radiation. The high resolution and
frequency tunability are perfect for investigating resonant behaviours around the relevant energies (carbon K-edge). Three different experimental spectrometer types were used, an ion-trap with a reflectron mass spectrometer,
hemispherical energy resolving electron analysers, and 3D momentum imaging spectrometers for charged particles.

Results: X-ray absorption like spectra were obtained for new ions, CH⁺₃ ,CH⁺₄ , and CH⁺₅ . The ionised versions
of CH_n revealed a much clearer picture of the various highly excited states which are not discernible in the neutral
variant. The fluxional nature of CH⁺₅ could be shown, as the spectrum was obtained from two geometrical
structures.

The resonant Auger-Meitner decay spectra of ethyl trifluoroacetate (ESCA) and cyclohexadiene (CHD) revealed
a clear state-selective process, and resonant behaviours.

The cyclic molecule cyclopropane showed different ring deforming dynamics dependent on which state was
excited (σ^* or π^*). A specific dynamic in cyclopropane was also found, which was the roaming dissociation
mechanism. The roaming was imaged with a 3D momentum spectrometer, and its existence was evident. This
roaming motion leads to the formation of the H⁺₃ ion.

• author: Lindblom, Ville
• supervisor: Stacey Ristinmaa Sörensen
• opponent: Professor Naves de Brito, Arnaldo, University of Campinas, Campinas, Brazil
• organization: Synchrotron Radiation Research; LU Profile Area: Light and Materials; Computational Chemistry; LTH Profile Area: Photon Science and Technology; Lund Laser Centre, LLC
• publishing date: 2026
• type: Thesis
• publication status: published
• subject: Physical Sciences; Atom and Molecular Physics and Optics
• keywords: synchrotron radiation, multi-coincidence, fragmentation dynamics, molecular roaming, ion spectroscopy, x-ray absorption spectroscopy, photoelectron spectroscopy, Auger-Meitner decay, Auger electron spectroscopy
• defense location: Lundmarksalen, Astronomy building, Sölvegatan 27. Lund
• defense date: 2026-05-20 13:00:00
• ISBN: 978-91-8104-952-7
• ISBN: 978-91-8104-951-0
• language: English
• LU publication?: yes
• id: 5d1bc1bc-39b3-40ac-93f3-18a4e15002cf
• date added to LUP: 2026-04-20 10:26:30
• date last changed: 2026-04-21 03:25:58