Photon induced inner-shell excitation processes of nitrous oxide probed by angle resolved fluorescence and Auger-Electron spectrometry

Knie, André

kassel university press, ISBN: 978-3-86219-458-2, 2013, 178 Pages

URN: urn:nbn:de:0002-34597

Zugl.: Kassel, Univ., Diss. 2012

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Content: Nitrous oxide (NNO) is an asymmetric linear three-atomic molecule. The strong electronegativity of the oxygen introduces a chemical shift on the central nitrogen's electron orbitals, resulting in a 4 eV shift of the core shell levels of the central nitrogen atom compared to the terminal nitrogen atom. Due to this shift energetically overlapping resonances of the terminal and central nitrogen’s 1s electrons occur and may lead to quantum mechanical interference of states with differently localized core-holes.

The focus of the work is the investigation of the relaxation paths of NNO after excitation of differently localized inner-shell electrons. Several intermediate tasks were performed and described.

i) The electron impact induced fluorescence set-up for calibration of the spectrometer-detector combinations was installed. For two wavelength ranges (40 - 120 nm and 160 - 320 nm) calibration spectra of noble gases were recorded and interpreted. The spectra of NNO and its fragments were recorded for comparison with the spectra obtained after synchrotron radiation excitation.

ii) The inner-shell excitation was investigated in relative absorption cross sections, ionization yield and fluorescence excitation functions for different wavelength ranges over an energy range from 396 - 410 eV. It was found that the fragmentation of NNO is dependent of the site of the excitation. Fragmentation is more likely when the central nitrogen 1s - pi* resonance is excited compared to the same resonance of the terminal nitrogen. The fluorescence spectrum of NNO was recorded from 170 - 600 nm after inner-shell excitation. It could be shown that the fluorescence of singly ionized fragment molecules is apparent in the UV (170 - 300 nm) which was predicted before. The fluorescence of different vibronic transitions was investigated scanning along the resonances, and no enhancement of bending modes was observed. The angular anisotropy of the fluorescence was determined for different vibrational modes of the A-X transition of NNO+ and is in general agreement with calculations.

iii) The angular anisotropy of several Auger-decay channels was determined scanning over the resonance region. Here the differences to the calculations, that neglect all kinds of interference, seem to point to an interference of electronic states with differently localized core holes.

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