In this dissertation, I present electronic spectroscopy of a few biologically relevant species and their complexes with solvent molecules in the gas phase using a variety of techniques, including resonantly enhanced multiphoton ionization (REMPI), laser induced fluorescence (LIF), and zero kinetic energy (ZEKE) photoelectron spectroscopy. My work on several methylated uracils and thymines and thymine-water complexes alludes to a new interpretation with regard to the origin of the photostability of our genetic code. I believe that it is the water solvent that stabilizes the photophysical and photochemical behavior of these bases under UV irradiation. For systems that demonstrate vibrational resolution in the first electronically excited state (S₁) and the cationic state, I performed vibrational analysis of both states with the aid of ab initio and density functional calculations. These observations are explained in terms of the structural changes from the ground state to S₁ and further to the cation. To bridge results from the gas phase to the solution phase, I also report studies of supersonically cooled water complexes of the three isomers of aminobenzoic acid. Density functional theory calculations are carried out to identify structural minima of water complexes in the ground state. The solvation mechanism is investigated based on vibrational analysis of the S₁ state of the neutral complex and the shift of ionization thresholds with increasing water content. / Graduation date: 2005

Copper-organonitrogen complexes are studied by threshold photoionization and zero electron kinetic energy photoelectron spectroscopy. These complexes are prepared in pulsed laser vaporization supersonic molecular beams. Adiabatic ionization energies of the neutral species and vibrational frequencies of the neutral and ionic complexes were measured. Metal-ligand bond dissociation energies were obtained from the theoretical calculations or the experiments. More importantly, by combining the spectroscopic measurements, quantum chemical calculations, and spectral simulations, metal-ligand bonding structures are determined for copper complexes of diamines, pyridine, diazines, aminopyridines, polypyridines, and imidazole. The Cu-ethylenediamine, -(1,3-propanediamine), and -(1,4-butenediamine) complexes have been determined to be in a hydrogen-bond stabilized monodentate configuration. However, Cu atom binds to both two nitrogens in the methyl-substituted ethylenediamines. The change of the Cu binding from the monodentate to the bidentate mode arises from the competition between copper coordination and hydrogen bonding. Although pyridine, diazines, and imidazole molecules can function as a s-donor through the nitrogen atom, a p-acceptor or p-donor through six-membered or five-membered aromatic ring, only the s bonding mode is predicted by the theory and identified by the ZEKE spectroscopy. For aminopyridine molecules, s bonding through the sp2 or sp3 hybrid electron lone pair and p bonding through the pyridine ring are possible. Yet, the s bonding through the sp2 electron donation is calculated to be the strongest, and the Cuaminopyridine complexes formed by such bonding mechanism are identified by the experiments. Moreover, monodentate Cu-(4,4'-bipyridine), bidentate Cu-(2,2'-bipyridine) and Cu-(1,10-phenanthroline), and tridentate Cu-(2,2':6',2?-terpyridine) are established to be the most stable structure and are observed by experiments. It is surprising to find that the tridendate planar structure of Cu-(2,2':6',2?-terpyridine) changes to a twisted Cs structure upon ionization.

Transition metal-aromatic hydrocarbon complexes were generated in a supersonic jet and studied by zero electron kinetic energy (ZEKE) photoelectron spectroscopy and theoretical calculations. The target metal complexes were identified using time-of-flight mass spectrometry, and their ionization thresholds were located via photoionization efficiency spectroscopy. ZEKE spectroscopy was used to measure the ionization energies and vibrational frequencies of the metal complexes. Their electronic states and corresponding molecular structures were determined by comparing the experimental spectra to quantum chemical calculations and Franck-Condon simulations. In this dissertation, the metal complexes of four different aromatic hydrocarbon ligands were studied: benzene (bz), naphthalene (np), biphenyl (bp) and 1-phenyl naphthalene (phnp). In these complexes, the metal atom or ion was determined to bind to either one or two -rings. Three different bonding schemes were observed in these complexes. A twofold bonding scheme was observed in M+/M-np (M = Sc, Y, Ti, Zr, Hf), while a sixfold bonding scheme was observed in Sc+/Sc-bz and M+/M-bz2 (M = Sc, Ti, V, Cr, Mo, W). In the metal-polyphenyl complexes (i.e. Sc-, La-, and Ti-bp and Sc-phnp), twelve-fold metal-ligand bonding occurred, sixfold to two -rings of the ligand. This twelve-fold bonding mechanism requires rotation of the -rings by ~ 42 o and bending of the -rings by 40 to 57 o to clamp the metal atom or ion between the two -surfaces. Although the ground state spin multiplicities of the bare metal atoms and ions varied quite extensively, the multiplicities of the metal complexes were determined to be either singlet or doublet, except for Sc+/Sc-bz, V+-bz2, Ti-np, and Zr-np, where the triplet or quartet spin multiplicities were favored. The low spin and relatively narrower range of electron-spin multiplicities in the complexes were the result of d orbital splitting, where the degeneracy of the d orbitals was broken. Thus, the valence electrons were paired in each metal d-based molecular orbital of the complex to form low-spin singlet or doublet spin states. Some complexes favored triplet and quartet multiplicities, because the energy difference between the two highest occupied molecular orbitals was smaller than the electron pairing energy.

Metal-cyclic hydrocarbon complexes were prepared in a laser-vaporization molecular beam source and studied by single-photon zero electron kinetic energy (ZEKE) and IR-UV resonant two-photon ionization (R2PI) spectroscopy. The ionization energies and vibrational frequencies of the metal complexes were measured from the ZEKE spectra. Metal-ligand bonding and low-lying electronic states of the neutral and ionized complexes were analyzed by combining the ZEKE measurements with density functional theory (DFT) calculations. In addition, C-H stretching frequencies were measured from the R2PI spectra. In this dissertation, metal complexes of 1, 3, 5, 7-cyclo-octatetraene (COT), toluene, p-xylene, mesitylene, hexamethylbenzene, biphenyl, naphthalene, pyrene, perylene, and coronene were studied. For each metal-ligand complex, different effects from the metal coordination have been identified. Although free COT is a nonaromatic molecule with a tub-shaped structure, the group III transition metal atoms (Sc, Y, and La) donate two electrons to a partially filled π orbital of COT, making the ligand a dianion. As a result, metal coordination converts COT into a planar, aromatic structure and the resulting complex exhibits a half-sandwich structure. For the Sc(methylbenzene) complexes, the benzene rings of the ligands are bent and the π electrons are localized in a 1, 4-diene fashion due to differential Sc binding with the carbon atoms of the rings. Due to differential metal binding, the degenerate d orbitals split and the Sc-methylbenzene complexes prefer the low-spin ground electronic states. In addition, as the number of methyl group substituents in the ligand increases, the ionization energies (IEs) of the Sc-methylbenzene complexes decrease. However, Ti, V, or Co coordination does not disrupt the delocalized π electron network within the carbon skeleton in the high-spin ground states of the metal complexes. For group VI metal (Cr, Mo, and W)-bis(toluene) complexes, methyl substitution on the benzene ring yields complexes with four rotational conformers of 0°, 60°, 120°, and 180° conformation angles between two methyl groups. In addition, variable-temperature ZEKE spectroscopy using He, Ar, or their mixtures has determined the totally eclipsed 0° rotamer to be the most stable. When there are two equivalent benzene rings, the metal (Ti, Zr or Hf) binds to both the benzene rings of biphenyl, or the metal (Li) binds to one of the benzene rings of naphthalene. On the other hand, the metal (Li) favors the ring-over binding site of the benzene ring with a higher π electron content and aromaticity in pyrene, perylene, and coronene.

Metal-hydrocarbon complexes were prepared in a laser-vaporization molecular beam source and studied by single-photon zero electron kinetic energy (ZEKE) and mass-analyzed threshold ionization (MATI) spectroscopy. The ionization energies and vibrational frequencies of the metal complexes were measured from the ZEKE and MATI spectra. Metal-ligand bonding and low-lying electronic states of the neutral and ionized complexes were analyzed by combining the spectroscopic measurements with quantum chemical calculations and spectral simulations. In this dissertation, the metal complexes of mesitylene, aniline, cyclooctatetraene, benzene, ethene, and propene were studied. For each complex, different effects from metal coordination have been identified. Although metal-bis(mesitylene) sandwich complexes may adopt eclipsed and staggered conformations, the group VI metal-bis(mesitylene) complexes are determined to be in the eclipsed form. In this form, rotational conformers with the methyl group dihedral angles of 0 and 60° are identified for the Cr complex, whereas the 0° rotamer is observed for the Mo and W species. The unsuccessful observation of the 60° rotamer for the Mo and W complexes is the result of its complete conversion to the 0° rotamer in both He and He/Ar carriers. For group III metal aniline complexes, the ZEKE spectrum of each complex exhibits a strong origin band, a short M+-aniline stretching progression, and several low-frequency ligand based vibrational modes. The intensities of most of the transitions can be explained by the Franck-Condon (FC) principle within the harmonic approximation. However, the intensity of the low frequency out-of-plane ring deformation mode is greatly overestimated by the FC calculations and may be caused by the anharmonic nature of the mode. Although aniline offers two possible binding modes for the metal atoms, a п binding mode is identified with the metal atom over the phenyl ring. For Ce, Pr, and Nd(cyclooctatetraene) complexes multiple band systems are observed. This is assigned to the ionization of several low-lying electronic states of the neutral complex. This observation is different from the Gd(cyclooctatetraene) complex, for which a single band system is observed. The presence of the multiple low-energy electronic states is caused by the splitting of the partially filled lanthanide 4f orbitals in the ligand field. The ZEKE spectrum of the Gd(benzene) complex exhibits a strong origin band, whereas the spectrum of Lu(benzene) displays a weak one. The benzene ring is planar in the Gd complex, but bent in the Lu complex. Dehydrogenation and C-C coupling products are observed in the reaction of La atom and ethene/propene. For the La and ethene reaction, La(C2H2) and La(C4H6) complexes are identified. With propene, C-H bond activation leads to the formation of the La(C3H4) and H-La(C3H5) complexes, whereas the C-C coupling yields the La(trimethylenemethane) complex. In addition, the La(CHCCH3) and La(CHCHCH2) isomers of La(C3H4) are observed, which are produced by the 1,2- and 1,3-hydrogen elimination of propene.

In dieser Arbeit werden kleine Schwefelcluser (S2 bis S8) untersucht. Es werden Massenspektren von gasförmigem Schwefel in Abhängigkeit von der Temperatur und der anregenden Photonenenergie vorgestellt. Es werden Photoionenausbeuten der Schwefelcluster im Anregungsenergiebereich der S 2p- und S 2s-Kante vorgestellt. Zudem werden Dreifachkoinzidenz-Experimente mit resonanter S 2p-Anregung durchgeführt.Diese experimentellen Techniken werden angewandt um die geometrische und elektronische Struktur, sowie die Fragmentationswege von einfach und mehrfach geladenen Schwefelclustern im Anregungsbereich der S 2p-Kante zu studieren. Die Photoionenausbeuten werden mit simulierten Photoabsorptionsspektren verglichen, die mit semiempirischen Extended-Hückel-Rechnungen ebenfalls im Rahmen dieser Arbeit bestimmt werden. Sie ermöglichen es, aus den Absorptionsquerschnitten im Bereich der Valenzübergänge Informationen über die Geometrie des Schwefelclusters zu erhalten.Vervollständigt wird die Arbeit durch die Untersuchung der besetzten elektronischen Niveaus. Es werden die S 2p-Ionisationsenergien von S2 und S8 untersucht. Dabei kommt eine Technik der Nullvolt-Photoelektronen-Spektroskopie zum Einsatz, bei der die Photoelektronen gemessen werden, die nach S 2p-Anregung auf das Ionisationspotenzial angehoben werden und somit keine kinetische Energie besitzen. Die Technik ist als ZEKE-Photoelektronen-Spektroskopie bekannt.

Ce travail a pour motivation de fournir des données expérimentales importantes pour l'interprétation de la chimie des ionosphère planétaires, en particulier pour le plus grand satellite de Saturne, Titan. On s'intéresse spécifiquement à la réactivité des espèces ioniques excitées. Cette thèse porte, d'une part, sur des expériences de préparation des cations (CH3+ et CF3+) sélectionnés en énergie interne par photoionisation VUV d'espèces neutres, et d'autre part, sur des réactions de cations sélectionnés en énergie interne avec des molécules, O+ avec CH4 et N+(3P) avec C3H4, C3H6 et C3H8.L'étude de la préparation des cations CH3+ et CF3+ sélectionnés dans des niveaux vibrationnels a été réalisée par la technique de coïncidence TPEPICO et du rayonnement VUV synchrotron à SOLEIL. Un spectromètre de type PFI-ZEKE qui permet d'atteindre une résolution de 0.84 cm-1 a été construit pour la réalisation d'études complémentaires avec le rayonnement laser VUV du Centre Laser de l'Université Paris Sud (CLUPS), à Orsay en France.Les expériences pour la détermination de l'influence de l'excitation du cation O+ (2S,2D,2P) sur sa réactivité avec le méthane ont été réalisées par les techniques de coïncidence TPEPICO et de guides d'ions. Elles ont été réalisées sur la ligne de rayonnement VUV DESIRS du synchrotron SOLEIL. Les études pour déterminer la constante de vitesse et les rapports de branchement entre produits des réactions de N+(3P) avec C3H4, C3H6 et C3H8 ont été réalisées par l'utilisation de la technique SIFT sur un montage de type commercial de petite taille à l'Institut de Physico-Chimie J. Heyrovský à Prague, en République Tchèque. / This work has the motivation to provide experimental data relevant to the interpretation of the chemistry of planetary ionospheres, particularly for the largest satellite of Saturn, Titan. Here we have a particular interest in studying the reactivity of excited ionic species. The first part of this work concerns the production of CH3+ and CF3+ state selected cations by VUV photoionization of neutral species and the second part, the reactions of state selected cations with molecules: O+ with methane and N+(3P) with C3H4, C3H6 and C3H8.The study of the preparation of the CH3+ and CF3+ cations in selected vibrational levels was performed by using the TPEPICO coincidence technique and VUV radiation at the french synchrotron, SOLEIL. A PFI-ZEKE spectrometer, that allowed us to obtain a resolution down to 0.84 cm-1, was constructed to conduct additional studies involving laser VUV radiation at the Laser Center of the University Paris Sud XI, at Orsay in France.Experiments to determine the influence of the O+ (2S,2D,2P) cation excitation on its reaction with methane were performed using the TPEPICO coincidence and the guide ion beam technique. These experiments were performed on the VUV DESIRS beamline at the synchrotron SOLEIL. Rate constants and products branching ratio for the reacion of N+(3P) with C3H4, C3H6 and C3H8 were measured with the SIFT technique in a small commercial apparatus at the Institute of Physical Chemistry J. Heyrovský in Prague, Czech Republic. / Este trabalho tem como motivação fornecer dados experimentais importantes para a interpretação da química de ionosferas planetárias, em particular para o maior Satélite de Saturno, Titan. Aqui temos o interesse específico pelo estudo de reatividades de espécies iônicas excitadas. Uma parte deste trabalho consistiu de experiências de preparação de cátions (CH3+ e CF3+) selecionados em energia interna via a fotoionização VUV de espécies neutras e de reações de cátions selecionados em massa e energia interna com moléculas (O+ com metano e N+(3P) com C3H4, C3H6 e C3H8).O estudo de preparação dos cátions CH3+ e CF3+ selecionados energia interna (vibracional) foi realizado pela utilização da técnica de coincidência TPEPICO com a radiação VUV do síncrotron SOLEIL. Um espectrômetro do tipo PFI-ZEKE que nos permite obter uma resolução de até 0.84 cm-1 foi construído para a realização de estudos complementares envolvendo a radiação VUV laser do Centro de Laser da Universidade Paris Sud XI, em Orsay na França.Experiências para determinar a influência da excitação do cátion O+ (2S,2D,2P) na produção de íons devido a sua reação com o metano foram realizadas com a utilização da técnica de coincidência TPEPICO e da técnica de guia de íons. Estes experimentos foram realizados na linha de radiação VUV DESIRS do síncrotron SOLEIL. Estudos de determinação de constantes de velocidade e dos produtos formados da reação N+(3P) com C3H4, C3H6 e C3H8 foram realizados a partir da utilização da técnica SIFT em uma montagem do tipo comercial de pequeno porte no Instituto de Físico-Química J. Heyrovský em Praga, na República Checa.

Ce travail a pour motivation de fournir des données expérimentales importantes pour l'interprétation de la chimie des ionosphère planétaires, en particulier pour le plus grand satellite de Saturne, Titan. On s'intéresse spécifiquement à la réactivité des espèces ioniques excitées. Cette thèse porte, d'une part, sur des expériences de préparation des cations (CH3+ et CF3+) sélectionnés en énergie interne par photoionisation VUV d'espèces neutres, et d'autre part, sur des réactions de cations sélectionnés en énergie interne avec des molécules, O+ avec CH4 et N+(3P) avec C3H4, C3H6 et C3H8.L'étude de la préparation des cations CH3+ et CF3+ sélectionnés dans des niveaux vibrationnels a été réalisée par la technique de coïncidence TPEPICO et du rayonnement VUV synchrotron à SOLEIL. Un spectromètre de type PFI-ZEKE qui permet d'atteindre une résolution de 0.84 cm-1 a été construit pour la réalisation d'études complémentaires avec le rayonnement laser VUV du Centre Laser de l'Université Paris Sud (CLUPS), à Orsay en France.Les expériences pour la détermination de l'influence de l'excitation du cation O+ (2S,2D,2P) sur sa réactivité avec le méthane ont été réalisées par les techniques de coïncidence TPEPICO et de guides d'ions. Elles ont été réalisées sur la ligne de rayonnement VUV DESIRS du synchrotron SOLEIL. Les études pour déterminer la constante de vitesse et les rapports de branchement entre produits des réactions de N+(3P) avec C3H4, C3H6 et C3H8 ont été réalisées par l'utilisation de la technique SIFT sur un montage de type commercial de petite taille à l'Institut de Physico-Chimie J. Heyrovský à Prague, en République Tchèque.