Vodík v molekulární a atomární formě je nejčastější prvek ve vesmíru a proto jsou chemické reakce, ve kterých vystupuje, důležité pro pochopení nejen formace prvních hvězd a galaxií, ale i pro studium současných dějů v mezihvězdném plynu. Studium například reakce H- + H -> H2 + e- (asociativní odtržení) ujasňuje náhled na proces tvorby molekul vodíku a umožňuje upřesnění kvantově-mechanických modelů. Pro tento a další experimenty je na KFPP přítomen zdroj chladného atomárního vodíku. V práci je popsána aparatura zdroje a její operace, navrhováno a částečně realizováno zlepšení uspořádání vnitřní konstrukce a jsou proměřeny základní charakteristiky zdroje.

The differential and total inelastic cross sections for electron-mercury atom collisions were calculated using the Born approximation together with the Ochkur approximation for the transitions (^1S_0 -> ^3P_0), (^1S_0 -> ^3P_2), (^3P_0 -> ^1S_0), and (^3P_2 -> ^1S_0) at one eV energy intervals from 1 eV - 33 eV above threshold. A reprint of work previously published containing values for polarizabilities of all the atoms is contained in Appendix B.

Since Swiatoslaw Trofimenko first reported their synthesis in 1966, poly(pyrazolyl)borate ligands, [R”ₓB(pz，ᴿ⋅ᴿ’)₄₋ₓ], have found widespread utility in modern coordination chemistry, undoubtedly as a consequence of the numerous facets of the ligand scaffold that can be readily altered. Relative to the extensive efforts directed towards the incorporation of pyrazolyl moieties with different substituents and towards the installation of groups other than hydrogen on the bridgehead boron, comparatively few attempts have been dedicated to elucidating synthetic approaches to altering the identity of the bridgehead atom itself. Such manipulations have the potential to generate new compounds that exhibit both structural and electronic properties previously unobserved or inaccessible for the parent boron compound, and the research summarized herein is motivated both by the paucity of these derivatives and by this potential. Chapter 1 explores the use of aluminum and gallium as linker atoms to afford heavier congeners of traditional poly(azolyl)borates. This study has utilized LiEH₄ (E = Al, Ga) in place of LiBH₄, and significantly has afforded the first structurally characterized examples of tris(pyrazolyl)hydrogallates and of tris(pyrazolyl)methylgallates featuring substituted pyrazolyl groups. Moreover, the structures of {[R”ETpᴿ⋅ᴿ’]Li}₂ (E = Al, Ga) have been found to vary as a consequence of the identity of both the pyrazolyl substituents (R, R’) and the substituent on the linker atom (R”), and in some instances differ significantly from the structures of the corresponding boron derivatives. Additionally, the reactions of LiEH4 with tert-butylmercaptoimidazole, HmimBut, have afforded the first examples of tris(mercaptoimidazolyl) ligands to feature aluminum and gallium bridgeheads. The molecular structures of these derivatives similarly display interesting coordination modes which, in some cases, contrast greatly to those of the parent boron ligands. In Chapter 2, synthetic approaches for the preparation of novel dianionic tris(pyrazolyl) ligands, obtained via the use of magnesium and zinc as linker atoms, are summarized. Interestingly, the otherwise neutral {[MeMTpᴹᵉ²][Li₂]} fragment is found to associate with an additional Lipzᴹᵉ² molecule, thereby affording a series of [MeMTpᴹᵉ²][Li3(pzᴹᵉ²)Ln] compounds in which each lithium is coordinated to two pyrazolyl nitrogen atoms. Both chloride and iodide anions can also serve as capping ligands for the {[MeMTpᴹᵉ²][Li₃]}+ moieties, suggesting that the trilithio scaffold can be viewed as a trifold receptor for anions. Additionally, the tetrakis(pyrazolyl) derivatives, [(THF)2Li{μ-[M(pzᴹᵉ²)₄]}Li(THF)₂], have also been prepared and structurally characterized. Chapter 3 details the preparation, characterization, and reactivity of symmetric homodinuclear magnesium and zinc complexes, [MeM(pzᴹᵉ²)₃MMe]–, in which the two metal centers are bridged by three exo-bidentate pyrazolyl ligands. The bridging of two identical metal centers by more than two pyrazolyl groups is a rare structural motif, and so [MeM(pzᴹᵉ²)₃MMe]– represent important contributions to not only the chemistry of magnesium and zinc, but also to that of the pyrazolyl ligand. The reactivity of [MeZn(pzᴹᵉ²2)₃ZnMe]– towards protic reagents and trimethyltin halides has been investigated, and has most notably afforded a rare example of an anionic terminal zinc fluoride complex, [FZn(pzᴹᵉ²)₃ZnF]–. Additionally, the homodinuclear zinc hydride complex, [HZn(pzᴹᵉ²)₃ZnH]–, has been obtained and structurally characterized, and represents the first example of an anionic terminal zinc hydride compound. The spectroscopic characterization of both [HZn(pzMe2)₃ZnH]– and its isotopologue, [DZn(pzᴹᵉ²)₃ZnD]–, are summarized, as are the results of preliminary reactivity studies with CO2 and CS2, which suggest that insertion of these heterocumulenes into the Zn–H bonds is facile and affords, inter alia, zinc formate and zinc dithioformate species, respectively. Chapter 4 summarizes the exocyclic N-methylation of Nitron(S), a 1,2,4-triazole thione derived from Nitron. The molecular structures of both Nitron(S) and of the methylated derivative, Nitron(S)Me, are reported, and a comparison of metrical data indicates that (i) the structures of these thiones differ significantly from the dominant tautomer of Nitron and (ii) the structures of these thiones compare favorably with the NHC tautomer of Nitron. Analyses of these compounds using natural bond orbital (NBO) and natural resonance theory (NRT) methods are in accord with the experimental structures.

The physisorption of Kr on graphitic amorphous carbon (g-C) has been investigated using a statistical approach. The interaction energy calculation process (i) established a structural model of g-C and (ii) determined the adsorbate-adsorbate and the adsorbate-substrate interaction potentials on g-C. The structural model of g-C was divided into three regions. For the interaction potential between a Kr atom and a carbon atom the short and medium range order of g-C was described with a discrete medium model based on three ring clusters using ring statistics from Beeman's continuous random network C1120 model of g-C. For the intermediate distance region, Beeman's radial distribution function was used to model g-C. A homogenous and isotropic continuous medium model was used at large distances. The Kr-Kr and Kr-g-C interaction potentials used for Kr on g-C, which are pair-wise Lennard-Jones 6-12 potentials, are similar to Kr on graphite potentials. the validity of the model for g-C and the potentials were verified though calculations for Kr on graphite. Results compared favorably with recent literature values. The interaction energy calculation results for Kr on a g-C substrate assert that (i) Kr adlayers will form on g-C, (ii) the structure of the Kr adlayer is governed by the substrate corrugation at low coverage and by the Kr-Kr interaction at high coverage, and (iii) there is no direct relation between the structure of Kr adlayers on g-C and those on graphite. The average binding energy of Kr on g-C is comparable with that on graphite, but the corrugation of g-C is perhaps six times that of a graphite substrate. The wrinkling of the g-C surface, due to the presence of a distribution of 5-, 6-, and 7- membered rings, is responsible for this large corrugation of the g-C substrate.

Cette thèse présente les résultats issus de l’investigation de la réponse optique de la transition D2 du Rubidium 87 en fonction de la densité de l’ensemble atomique. Afin de sonder cette transition nous utilisons un faisceau laser proche de la résonance (780nm) sur un échantillon de Rubidium ultra-froid (100µK). Nous observons ainsi la transmission en fonction de la longueur d’onde pour des densités allant de 10^12 atomes/cm^3 à 10^14 atomes/cm^3. Lorsque la densité augmente, on s’attend à ce que les interactions dipôle-dipôle jouent un rôle de plus en plus important du fait de la proximité des éléments diffusants. Quantitativement, les dipôles induits par le faisceau sonde commencent à jouer un rôle important lorsque la densité n atteint n*(lambda/2Pi)^3 = 1, une densité que nous atteignons dans notre système.Deux études systématiques seront présentées. La première montre les résultats obtenus pour un système à 12 niveaux, la deuxième pour un système à 2 niveaux obtenu par polarisation de l’ensemble atomique. Les résultats issus de ces études sont ensuite comparés aux théories existantes. La première approche est microscopique et décrit les interactions des dipôles couplés, la deuxième approche, macroscopique, est donnée par l’équation de Clausius-Mosotti.Les propriétés de propagation d’impulsions à travers ce système sont étudiées et révèlent en particulier un avancement fractionnel de l’impulsion et un indice de groupe inégalés. / This thesis investigates the response of the D2 transition of Rubidium 87 for various densities.To probe this transition we illuminate an ultra cold (100µK) sample of Rubidium 87 with close toresonance of lambda = 780 nm laser light.We observe the transmitted light while scanning the frequency over the atomic resonance. Such a spectrum is taken for peak densities ranging from 10^12 atoms/cm^3 to 10^14 atoms/cm^3. As matter gets denser and denser dipoie-dipole interaction start playing a role due to the close proximity of neighbouring scatteres. These interactions are caused by the probe light induced dipoles and start being important when the density reaches n*(lambda/2Pi)^3 = 1, which for us is the case at the upper end of the explored density range.We start off measuring these transmission data for degenerate 12-level Rubidium 87 and afterwardsfor Rubidium 87, which we first spin polarize and then by lifting the degeneracy generate an artifical2-level system. These results are systematically compared to the two available theories.A microscopic one, which is described by coupled dipoles and a macroscopic one the so calledClausius-Mosotti equation. None of the ab initio theories can explain the results obtained during this thesis.The rigerous comparison of the various acquired datasets shows that the data in itself is consistentand relative changes going from a 12-level system to a 2-level system are understood.Additionally we also investigate the pulse propagation behaviour through such a systemrevealing stunning values for the fractional pulse advancement and the group index.

The purpose of this study was to investigate the difference between the “atoms first” and the “traditional” curricula. Specifically focusing on which curriculum better aligns to curricular expectations, leads to higher student success when students are grouped together, and when students are differentiated based on several factors. The main difference between the two approaches being the sequence of topics presented in the first semester general chemistry course. This study involves more than 9,500 general chemistry I and II students over 7 semesters with about half of them being taught using the “atoms first” approach. Student success was measured using the American Chemical Society’s (ACS) final examination scores and the final letter grades. Alignment to curricular expectations was determined via a qualitative review of textbooks written for each of the approaches. This showed that the “atoms first” approach better aligns to research supported best practices. An analysis of covariance (ANCOVA) was performed to determine if there is a significant difference between the “atoms first” and the “traditional” curricula. The “traditional” approach was found to lead to higher student achievement for both measures of student success in both chemistry I and II courses. Lastly, multiple linear, multinomial logistic, and binary logistic regressions were run using all of the subgroups – gender, race/ethnicity, major, ACT composite, math ACT, overall GPA, and classroom size – as predictor variables to determine if any significant interactions between the curricular methods and the different subgroups existed. Results found that the relationship between gender, GPA, and classroom size groupings significantly impact student achievement in general chemistry. Specifically, the “traditional” approach lead to higher student success compared to the “atoms first” approach for males, females, below average GPA students, above average GPA students, and students in large classroom settings. However, there are several factors – final examination content, new teacher impact, teacher’s view of science, and withdrawal rate and timing – that need to be taken into account when implementing these findings. Overall, the results of this study provides a cautionary reminder of the many impacts affecting curriculum implementation and the importance of professional development and training during a curriculum transitional period.

No description available.

<p> This thesis presents the theoretical study of the mechanisms of gas-phase formamide hydrolysis using ab initio SCF-MO calculations. Four reaction paths were considered; (i) the reaction of formamide with OH- (ii) the acid catalyzed hydrolysis with protonation on the nitrogen atom (iii) the acid catalyzed hydrolysis with protonation on the oxygen (iv) the uncatalyzed hydrolysis. An unconstrained optimization of all parameters was performed on the transition state and equilibrium structures. The intrinsic reaction coordinate was then followed down from the transition state to the reactants and products. All of the molecular geometries were obtained using the 4-31G basis set and all wavefunctions and energies were calculated at the 6-31G** level of theory. The theory of atoms in molecules was applied to each reaction to study the mechanisms of structural change along the reaction coordinate. Molecular graphs were calculated at points along the reaction coordinate and these give a detailed pictorial outline of the entire reaction sequence. The Laplacian of the charge density successfully predicts the correct site of protonation and the enhanced reactivity of protonated formamide over that of neutral formamide. Both the acid catalyzed reaction with nitrogen protonation and the base enhanced hydrolysis reactions proceed without a barrier with respect to reactants and products. The acid catalyzed hydrolysis with protonation on the oxygen atom proceeds with a moderate activation barrier whereas the neutral hydrolysis involves the passage over a very high activation barrier. The two acid catalyzed reactions are competitive with the N-protonation mechanism being more favourable from a kinetic point of view while the O-protonation mechanism is thermodynamically more favourable.</p> / Thesis / Master of Science (MSc)

<p> The crystal structures of VOP2SiO8, VO(PO3)2, V(PO3)3, (VO)2P2O7 and VAsO5 have been determined with the help of x-rays, and are compared with the known structures in the V-P-As-O system. All the vanadium atoms in the mixed oxides are octahedrally coordinated and the V^+4 O6 and V^+5 O6 octahedra are all characterized by one short vanadyl bond. V^+3 O6 groups are nearly regular. The tetrahedral phosphorus is found in structural elements ranging from infinite metaphosphate chains (V(PO3)3, VO(PO3)2), to pyrophosphate groups ((VO)2P2O7) to isolated tetrahedra (VAsO5 and VOP2SiO8). Both structural and substitutional disordering is evident in the V-P-As-O system, and is discussed together with a detailed model for stacking faults in VAsO5.</p> <p> Some of the phases in the V-P-As-O system are known to catalyze the oxidation of butene to maleic anhydride, and certain structural features of the compounds are related to this catalytic activity. α-VPO5 can be related to (VO)2P2O7 through the formation of shears in a manner similar to shear formation in V2O5, and such a mechanism is proposed as a means whereby an α-VPO5 catalyst can change into (VO)2P2O7, the known composition of the spent catalyst.</p> / Thesis / Doctor of Philosophy (PhD)

<p> Mn2P2O7 belongs to the monoclinic space group C2/m. The manganese atoms are six-fold coordinated to oxygen atoms forming distorted octahedra. The bonding in P2O7^4- ion is discussed with reference to values predicted by Cruickshank and Baur.</p> <p> The central oxygen atom in P2O7^4-ion shows enhanced motion, a feature common to all the members of the thortveitite series. By collecting X-ray data at -180°C, an attempt has been made to understand the nature of this enhanced motion.</p> / Thesis / Master of Science (MS)