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Femtosekunden Photolyse von Diiodmethan in überkritischen Fluiden: Konkurrenz zwischen Photodissoziation und Photoisomerisierung
| Content Provider | Semantic Scholar |
|---|---|
| Author | Grimm, Christian |
| Copyright Year | 2004 |
| Abstract | This thesis deals with effects that a dense fluid environment may have on the dynamics of elementary reactions such as competition between reactant escape from a solvent cage and in-cage reaction after photodissociation. This well known phenomenon proposed by Franck and Rabinowitsch in the mid 1930s is called "photolytic cage effect" and was intensively investigated in connection with the photodissociation of iodine.In this study we investigate the photolytic cage effect following the photodissociation of the polyatomic compound diiodomethane in supercritical fluid solution.Whereas in the gas phase this reaction is well understood, several aspects of the dynamics in condensed phase remain unclear. According to previous studies in matrices and liquid organic solvents using transient absorption techniques, subsequent to photodissociation the diiodomethane isomer is formed by geminate combination of iodine atoms and CH2I radicals within the original solvent cage.Within the framework of this thesis the kinetics and dynamics of the photolysis of CH2I2 in several supercritical fluids were investigated. Supercritical fluids present the possibility to continuously vary the solvent density between gas phase and liquid phase conditions. In this way density dependent absorption time profiles where obtained by femtosecond pump probe measurements. In addition, transient spectra were reconstructed from kinetics at different probe wavelengths.One of the main results of these investigations is that the yield of isomer shows a linear increase as a function of the reduced density in all solvents. This supports the view of a purely kinematic cage breakout of the fragments and is in accord with the interpretation of the photolytic cage effect in iodine photodissociation. The rate constant for the in-cage isomerization shows a nearly exponential growth with increasing solvent density. Several explanations for this behavior are discussed and a preliminary kinetic model is proposed. The model includes the competition between cage breakout of the fragments and the in-cage isomerization channel as well as the influence of vibrational energy relaxation on the isomerization yield and rate constant. Furthermore the species contributing to the short time signals are discussed in detail. |
| File Format | PDF HTM / HTML |
| Alternate Webpage(s) | https://ediss.uni-goettingen.de/bitstream/handle/11858/00-1735-0000-0006-AD49-8/grimm.pdf;jsessionid=EC127749E893C6DF4867027AC71A45C9?sequence=1 |
| Language | English |
| Access Restriction | Open |
| Content Type | Text |
| Resource Type | Article |
