Photoionisationsmassenspektroskopie primärer Photolyseprodukte

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Titel: Photoionisationsmassenspektroskopie primärer Photolyseprodukte
Sonstige Titel: Photoionization mass spectrometry of primary photofragments
Autor(en): Schürmann, Max Christian
Erstgutachter: Prof. Dr. E. Rühl
Zweitgutachter: Prof. Dr. W. Heiland
Zusammenfassung: A new experimental approach is reported that focuses on photoionization mass spectrometry of primary photofragments. Photodissociation of molecules and radicals is carried out by using a tunable, pulsed dye laser. Nascent photofragments are subsequently photoionized by time-correlated vacuum-ultraviolet (VUV) radiation, so that only single-photon ionization occurs. Several experimental approaches are used in order to optimize pulsed radiation sources in the VUV that are suitable for pump-probe experiments. Laser systems that rely on frequency tripling in suitable non-linear media are used as an intense VUV radiation source of narrow bandwidth and limited tuning range. Monochromatized laser-produced plasma radiation is also used, which provides tunable VUV radiation throughout the entire VUV energy regime (8-25 eV). Ionized photofragments are finally detected by time-of-flight mass spectrometry. This experimental approach is used in order to investigate the following issues: * Absolute photoionization cross sections of atomic and molecular photofragments are derived from photoionization mass spectrometry. This is shown for the photolysis of chlorine dioxide (OClO), chlorine monoxide (ClO) and ozone (O3). The latter species generates O(1D), so that photoionization and autoionization of this excited species was studied for the first time. * Quantum states and quantum state distributions are derived from photoion yields of primary photofragments in order to characterize photodissociation processes. This is shown for the predissociation of OClO, which yields vibrationally excited ClO in its electronic ground state. * Branching ratios and quantum yields of competing photochemical pathways are determined from photoionization mass spectrometry. The accuracy of this approach is superior to other techniques. These investigations allowed us to investigate photolysis processes of molecules and radicals that are of significant importance with respect to recent issues of atmospherical photoprocesses, such as polar ozone depletion.
Schlagworte: Mass spectrometry; photoionization; photodissociation; autoionization; vacuum-uv plasma source; quantum yields; ozone depletion
Erscheinungsdatum: 29-Jun-2001
Enthalten in den Sammlungen:FB04 - E-Dissertationen

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