FCT: DF - Teses de Doutoramento
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- Electron Transfer Processes in Biologically Relevant Molecules. An Experimental Study of Neutral Alkali Atom-Molecule CollisionsPublication . Kumar, Sarvesh; Limão-Vieira, PauloThe work developed within the context of this thesis includes negative ion formation in charge transfer processes from collisions of neutral potassium atoms with key selected neutral mole-cules. The crossed molecular beam set up used to obtain the anion yields as a function of the collision energy as well as relevant information about the lowest-lying anionic states that are accessed in the temporary negative ion formation, is fully equipped with a time−of−flight mass spectrometer and an energy loss analyser. The spectrometric technique includes a linear and a reflectron type time-of-flight mass spectrometers to provide information about the neg-ative ions formed in such collisions. We have made use of a home−built Wiley McLaren type Linear Time-of-flight mass spectrometer (L−TOF−MS), to extract relevant information about the kinetic energy release distribution of selected fragment anions, as a function of the collision energy, while the reflectron time−of−flight mass-spectrometer (r−TOF−MS) was used due to its higher mass resolution serving as a proper tool to resolve close lying fragment anions dif-fering by just 1 amu in the fragmentation of nimorazole. In order to obtain relevant infor-mation about the most accessed negative ion states in the collision process, a post−collision potassium cation (K+) energy loss spectra in the forward scattering direction (θ ≈ 0°) with the beam's optical path have been recorded in a hemispherical energy loss analyser. The combi-nation of TOF−MS and these two techniques helped us to gain deep insight into electron trans-fer processes of molecules under investigation. The set of chlorinated molecules investigated include a group (C6H5Cl,C6D5Cl, C6H11Cl,and C6Cl6) that has been properly chosen to explore the role of direct dissociation through electron transfer into a σCl∗ antibonding orbital and more importantly to determine the role of intramolecular electron transfer through π∗σCl∗⁄ coupling yielding anion formation. From the comprehensive investigation of these molecules in a wide energy range of collision energies, 10 − 103 eV in lab frame, we have obtained for the first time the relative cross−sec-tion for Cl− formation. The other group of molecules include biological relevant targets as the radiosensitizer nimorazole (NIMO) and water. Regarding the former, although the major signal is assigned to the non-dissociated parent anion (80% of the total anion yield), NO2− accounts for just 10−15% of the total anion yield a detailed trace fragmentation pattern indicates decomposition of NIMO's 4−nitroimidazole and morpholine rings. As far as the latter is concerned, H2O and its deuterated counterpart D2O were investigated and are presented in the third part of this thesis. The fragmentation pattern from H2O includes H−, O−, and OH− whereas from D2O in-cludes D−, O−, and OD−. From the different TOF mass spectra the fragment anions' thresholds of formation have been obtained. K+ energy loss spectra from NIMO, H2O and D2O were also recorded, revealing the experimental vertical electron affinities of the most accessed negative ion states.
- Implications of a polymer meniscus implant on knee tribologyPublication . Majd, Sara Ehsani; Busscher, H.; Sharma, P.; Kuijer, R.
- High precision tests of QED Measurement of the alpha-particle and helion rms charge radius and the transition energies in highly-charged ionsPublication . Machado, Jorge Felizardo Dias Cunha; Santos, José; Indelicato, PaulThis work aims to provide insight on Bound-State Quantum-Electrodynamics (BSQED) by experimental fundamentals high-precision tests in exotic states of matter. Although BSQED and the relativistic many-body problem have been undergoing important progress, there are still some issues that require the increase of the number and accuracy of experimental fundamental tests. The first part of this work was done within the framework of the recent experiment in muonic helium ions ( 4He+ and 3He+) by the CREMA collaboration. This experiment, aims to provide new accurate values for the root-mean-square (rms) charge radii of the helium isotopes nuclei that are extracted from the measurement of the Lamb Shift, i.e., the measurement of the energy difference between the 2S 2P states. With the goal of measuring the transition energies with an accuracy of at least 50 ppm, the rms charge radii of the helium isotopes will be determined with an uncertainty of 0.03%, a factor of ten more precise than previous results obtained from electron scattering. The second part of this work aims the high-precision measurement of x-ray transitions in Highly-Charged Ions (HCI) using a Double-Crystal Spectrometer (DCS). These ions were produced in the plasma of an Electron-Cyclotron Resonance Ion Source (ECRIS). This kind of spectrometer is able not only to provide high-precision measurements but also reference-free measurements, without reference to any theoretical or experimental energy. Four transitions energies from n = 2!n = 1 have been measured in an argon plasma in three different charge states, He-, Be- and Li-like, with an accuracy of better than 3 ppm. Besides the energies, the natural width of each transition has also been experimentally obtained. The obtained results are in excellent agreement with the most recent theoretical calculations.