@phdthesis{Matthaei2023,
  author    = {Matthaei, Christian Tobias},
  title     = {Studying the Photodissociation of Chlorine-Containing Molecules with Velocity Map Imaging},
  doi       = {10.25972/OPUS-32740},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-327405},
  school      = {Universit{\"a}t W{\"u}rzburg},
  year      = {2023},
  abstract  = {The first is via direct dissociation and the second likely involves a barrier slowing down dissociation. Chlorine-containing hydrocarbons pose a great risk for the environment and especially for the atmosphere. In this thesis I present the photodissociation dynamics of multiple chlorine-containing molecules. The method of velocity map imaging was utilized for gaining information on the kinetic energy distribution of the fragments generated in the photodissociation reactions. First, the photodissociation of benzoyl chloride after excitation to the S1, S2 and the S3 state between 279 nm and 237 nm was studied. This stable molecule was an ideal candidate for demonstrating a new ionization scheme for chlorine atoms. It was shown that benzoyl chloride dissociates statistically from the ground state. Afterwards, the results from experiments on the radicals trichloromethyl and dichlorocarbene are presented in the range of 230 to 250 nm. These radicals remain after the dissociation of carbon tetrachloride and have not been studied in detail because of their instability. Trichlormethyl dissociates via two paths: The loss of a chlorine atom to dichlorocarbene and by decaying to CCl and a chlorine molecule. The dissociation to dichlorocarbene involves a barrier. If the photon exciting the molecule has enough energy to surpass the barrier, which is the case starting at around 235 nm, trichlormethyl dissociates rapidly resulting in an anisotropic VMI. However, if the the excitation energy is lower, the dissociation takes longer than a rotational period and the anisotropy is lost.The path to CCl is a statistical dissociation. Dichlorocarbene dissociates to CCl and Cl via to separate channels. The first is via direct dissociation and the second likely involves a barrier slowing down dissociation.},
  subject      = {Photodissoziation},
  language  = {en}
}
@phdthesis{Andrei2007,
  author    = {Andrei, Horia-Sorin},
  title     = {Infrared photodissociation spectroscopy of ionic hydrocarbons : microsolvation and protonation sites},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-24652},
  school      = {Universit{\"a}t W{\"u}rzburg},
  year      = {2007},
  abstract  = {This work has presented a spectroscopic analysis of three types of hydrocarbon cations: two ionized aromatic hydrocarbons, two protonated aromatic hydrocarbons and the cation of a fundamental radical hydrocarbon. The experiments were centered on the proton stretch vibrations of mass-selected complexes of these systems and polar (H2O) and non polar (Ar, N2, CO2) ligands. The experiments have been done in a tandem mass spectrometer coupled with an electron impact ionization ion source; an OPO laser system was used as tunable IR light source. All the proposed dimer structures have been also modeled using quantum chemical calculations (QCC). These calculations have consistently been matched with the experimental results and have enabled clear identification of the spectral features observed. This has enabled the evaluation of thermochemical properties which could not be extracted directly from experiment. The experiments done on complexes of 1-Np+ and Im+ have allowed for the acidity of their various groups to be probed: the shifts in the frequency as well as the enhancement in the intensity of the OH and NH stretch vibrations resulting from the complexation have yielded dependences on both the species (L) and the number (n) of the ligands. OH bound 1-Np+···Ar has been detected for the first time, showing that the REMPI-IRPD method is severely limited with respect to the production of the most stable isomer of a given cationic complex. The detection of c-1-Np+···(N2)n corresponds to the first observation of c-1-Np+ complexes and enables thus direct comparison of both 1-Np+ rotamers. The shift of the NH vibration of Im+···N2(H) yielded the first experimental estimate for the PA of the imidazyl radical. It was also found that the most stable 1-Np+···Ar and Im+···Ar structures differ qualitatively from that of the corresponding neutral dimers (H-bound vs pi-bound), emphasizing the large impact of ionization on the interaction potential and the preferred recognition motif between acidic aromatic molecules (A) and nonpolar ligands. The IRPD spectra of 1-Np+···Ln and Im+···Ln yielded spectroscopic information about the CH, NH and OH stretch vibrations of bare 1-Np+ and Im+. The dependence of the shifts in the frequency of the OH and NH stretch vibrations allows for creating microsolvation models. The spectroscopic results obtained on size-selected 1-NpH+···Ln show that, in the output of the presently used ion source, three classes of 1-NpH+ isomers can be identified: oxonium ions (1-Np protonated at the O atom); carbenium ions obtained by protonation in the para and ortho positions with respect to the OH functional group; carbenium ions obtained by the addition of a proton to well-defined sites on the second naphthalene ring. The spectral identification of these three classes of protonation sites is supported by their different photofragmentation patterns. It was demonstrated that the spectroscopic monitoring of the microsolvation of ImH+ in Ar and N2 together with the QCCs paint a very detailed picture of the microsolvation process, evidencing clear differences between the microsolvation models as function of the PA of the ligands. Important differences have also been identified between the various binding sites, enabling the creation of a clear scale of priorities for occupation of the binding sites during microsolvation. The application of IRPD to the study of microhydrated ImH+ provided for the first time direct spectroscopic information on the properties of the N-H bonds of this biomolecular building block under controlled microhydration. It was demonstrated that, as protonation enhances the acidity of the NH groups, the ability for proton conductivity of ImH+ increases. A very important result is derived from the IRPD spectroscopy of C2H5+···L (L = Ar, N2, CO2, CH4) dimers. The equilibrium geometry of the C2H5+ has long been debated. Now, IRPD spectra were recorded over the range of the CH stretch fundamentals (covering possible sp3 and sp2 hybridization of C). Depending on the ligand species, the spectra are found to be dominated by the fingerprint of two largely different dimer geometries. Using the experimental C2H5+···Ar spectrum and the corresponding QCCs, the structure of the (weakly perturbed) C2H5+ was found to be the nonclassical one, with one proton straddling across the C=C bond of the H2C=CH2. On the other hand, ligands like N2 and CH4 are strongly influencing the geometry, as seen in the spectral signatures of the C2H5+···N2 and C2H5+···CH4, which correspond to the classical [H2CCH3]+. It was thus demonstrated that while the nonclassical C2H5+ is the global minimum on the PES of the free [C2,H5]+, the structure of the C2H5+ can be strongly influenced by the chemical properties of the environment.},
  subject      = {Infrarot},
  language  = {en}
}