Anion Photoelectron Spectroscopy of Small Clusters PDF Download

Author: Sean Michael Sheehan
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Category :
Languages : en
Pages : 316

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Author: Harry Gomez
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Category :
Languages : en
Pages : 482

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Author: Kim Marlies Liliane Lapere
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Languages : en
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[Truncated] Ion-molecule clusters comprising a halide anion 'core' solvated by neutral molecules in the gas phase are characterised using anion photoelectron spectroscopy and ab initio computational techniques. These clusters are of interest in studying the e ects of di erent solvent molecules on small anion cores, as transition states in reactions and are of atmospheric relevance. Many of these have not previously been investigated using the techniques employed in this work, as such the results presented here are novel. The mass and photoelectron spectra obtained for this dissertation include Cl-...(N2)n, Br-...(N2)n, I-...(N2)n, Br-...(N2O)n, Cl-...(NO)n, Br-...(NO)n and I-...(NO)n. The spectra were recorded using a home-built time-of- ight photoelectron spectrometer coupled to a time-of- ight mass spectrometer. Although the photoelectron spectra are of low resolution, the stabilisation energies and electron anities for these clusters of interest have been extracted. These are compared to analogous studies from the literature, such as the uoride clusters. The limits for the rst solvation shell of each of the clusters were determined to be larger than the sizes of the clusters under investigation here.

Author: Travis Robert Taylor
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Languages : en
Pages : 356

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Author: Cangshan Xu
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Category :
Languages : en
Pages : 402

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Author: David Yubero Valdivielso
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Category :
Languages : en
Pages : 0

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Author:
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Category :
Languages : en
Pages : 175

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Anion photoelectron spectroscopy is used to study free radicals and clusters. The low-lying 2[Sigma] and 2[pi] states of C2nH (n = 1--4) have been studied. The anion photoelectron spectra yielded electron affinities, term values, and vibrational frequencies for these combustion and astrophysically relevant species. Photoelectron angular distributions allowed the author to correctly assign the electronic symmetry of the ground and first excited states and to assess the degree of vibronic coupling in C2H and C4H. Other radicals studied include NCN and I3. The author was able to observe the low-lying singlet and triplet states of NCN for the first time. Measurement of the electron affinity of I3 revealed that it has a bound ground state and attachment of an argon atom to this moiety enabled him to resolve the symmetric stretching progression.

Author: Etienne Garand
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ISBN:
Category :
Languages : en
Pages : 528

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The anion slow photoelectron velocity-map imaging (SEVI) technique, a high resolution (̃1 cm-1) variant of anion photoelectron spectroscopy, is applied to the study of open-shell anions and neutral species. First, SEVI is used to study the CnH (n=5-9), C2nN (n=1-3), CnO (n=2-3) and CnS (n=2-3) heteroatom doped carbon clusters. The SEVI spectra are assigned with the help of electronic structure calculations and Franck-Condon simulations. Precise electron affinities, term energies and vibrational frequencies are determined for these species. These studies also yield evidence of vibronic coupling in the ground states of C6H, C8H, C9H and CCS. Futhermore, it is found that the ground states of the C5H-;, C7H-;, C7H-;, C4N-; and C6N-; anions are linear triplet sigma states, contrary to previous theoretical studies that reported bent structures. In addition, the strong vibronic coupling between the very close-lying 2A1 and 2B2 states of the HCO2 and DCO2 radicals is studied using SEVI. The complex photodetachment spectra are simulated and assigned using a quasidiabatic Hamiltonian approach. The strong vibronic coupling is highlighted by the observation of several nominally forbidden transitions. The SEVI technique is also applied to the study of the weakly bound ArO and KrO van der Waals complexes. The interaction potential and spin-orbit splitting of the neutral and anion states are determined and compared with high-level electronic structure calculations. Finally, the SEVI spectra of the ClH2-; and ClD2-; anions are used to characterized the electronic and nuclear coupling in the pre-reactive region of the Cl(2P)+H2 reaction and to understand the reactivity of the excited spin-orbit state of chlorine. The SEVI spectra are compared to simulations with and without non-adiabatic couplings between the Cl spin-orbit states. The non-adiabatic effects are found to be small but their inclusion improves agreement with experiment. The second part of this work concerns the structure of ionic clusters which is studied with infrared multiple photon dissociation (IRMPD) spectroscopy. The stepwise solvation of the bicarbonate anion is probed by acquiring the IRPMD spectra of HCO3-(H2O)1-10 clusters in the gas-phase. Electronic structure calculations have been performed on the n=1-8 clusters to identify the structure of the low-lying isomers and to assign the observed spectral features. It is found that the water molecules preferably bind to the negatively charged CO2 moiety of the HCO3 & hibar; anion. A binding motif consisting of a four-membered ring with each water forming a single H-bond with the CO2 moiety is found for clusters with n=4 or larger. In addition, the structure of the small (SiO)3-5+ clusters have been studied with IRPMD and electronic structure calculations. The onset for the formation of the first Si-Si bond is observed for the n=5 cluster.

Author: Simson Alex
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ISBN:
Category :
Languages : en
Pages : 386

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Author: Alexandra M. Vlk
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Category :
Languages : en
Pages : 94

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Photoelectron spectra (PES) are generated by crossing a mass selected beam of negative ions with a beam of photons from an Argon ion laser which causes photodetachment of electrons. These electrons are energy analyzed yielding a photoelectron spectrum that can be analyzed in accordance with the electronic transitions between the anion ground state and the neutral ground and excited states. Molecular properties determine how tightly the electron is held and how easily it detaches. Data collected from various systems are presented here. Most notably are the 2-hydroxypyridinedimer system and the proton sponge with ethylene glycol systems. Preliminary data on other systems are also provided: proton sponge with HCl and proton sponge with 1-propanol. The 2-hydroxypyridine anionic dimer was investigated because of its resemblance of nitrogenous heterocyclic nucleobases of DNA. The experimentally measured vertical detachment energy (VDE) of 1.21 eV compares well with the Density Functional Theory (DFT) calculated values indicating electron induced proton transfer (EIPT). Models of EIPT from the neutral lactim and lactam homogeneous tautomer dimers show that, upon electron attachment, the anionic result can serve as the intermediate between the two neutral dimers. This potential electron catalyzed double proton transfer mechanism of tautomerization can be applied to our understanding of electron damage to biological systems such as DNA point mutations caused by tautomeric shifts. The proton sponge with ethylene glycol system was chosen to examine the EIPT boundary in anionic systems based on the empirical formula derived by Alkorta, et. al. PES data indicates possible proton transfer and solvent stabilization, to be confirmed by DFT calculations.