Rotationally averaged polarizabilities and intrinsic electric dipole moments of sodium clusters are measured and reported. The experimental method is a molecular beam deflection. Our precision is the highest (<5%) and the range of the cluster sizes is the broadest to date (Na₁₀ ∼ Na₃₀₀). Compared to the earlier measurements, our data covers all sizes with no gaps up to the largest cluster. The fine structure in the polarizability curve is previously unobserved. We have carefully ruled out several possible explanations. And we find an earlier existing theory could explain the facts but will lead to magic numbers which were not seen in some previous experiments. A detailed theory is needed to understand the behaviors we see. Intrinsic electric dipole moments (EDM) of sodium clusters are probed to answer the intriguing question: Do metal clusters develop electric dipole moments like molecules? Some theories have predicted the existence of EDM in ground state sodium clusters and gave their magnitudes. We put upper bounds on the EDM of sodium clusters and find that they are orders of magnitude smaller than the predictions. This provokes an interesting question: how can one define metallicity in metal clusters? Our measurements are performed at cryogenic temperature 20 Kelvin. At this temperature the clusters are believed to be in their vibronic ground states.

No description available.

Αντικείμενο της παρούσης διδακτορικής διατριβής αποτελεί ο υπολογισμός των ηλεκτρικών πολυπολικών ροπών (διπολική έως και δεκαεξαπολική) ακετυλενικών αλυσίδων οι οποίες υπάγονται στους γενικούς τύπους H-(C≡C)n-H, Χ-(C≡C)n-H και Χ-(C≡C)n-X, n=1–7, X=F, Cl, Br, I, CN, NC, η συστηματική μελέτη των (υπερ)πολωσιμοτήτων των μη υποκατεστημένων ακετυλενικών αλυσίδων Η-(C≡C)n- H, n=3–7 και τέλος ο υπολογισμός των ηλεκτρικών ιδιοτήτων αλληλεπίδρασης συστημάτων του τύπου Η-(C≡C)n-H…Ηe, n=1–7. Σε όλες τις περιπτώσεις χρησιμοποιήθηκαν οι ab initio μέθοδοι SCF και MP2 καθώς και οι ευρέως χρησιμοποιούμενες DFT μέθοδοι B3LYP, B3PW91 και mPW1PW91. Στους υπολογισμούς των ηλεκτρικών πολυπολικών ροπών χρησιμοποιήθηκε η βάση ccpVDZ σε όλες τις περιπτώσεις και ιδιαίτερη έμφαση δόθηκε στον τρόπο μεταβολής των υπό μελέτη ιδιοτήτων με την μεταβολή του υποκαταστάτη στα άκρα της αλυσίδας. Στους υπολογισμούς των ηλεκτρικών (υπερ)πολωσιμοτήτων των μη υποκατεστημένων ακετυλενικών αλυσίδων Η-(C≡C)n-H χρησιμοποιήθηκαν ελάχιστα πολωμένα σύνολα βάσης και πραγματοποιήθηκε σύγκριση με τα αποτελέσματα που προέκυψαν από την χρήση μεγαλύτερων συνόλων βάσης. Για τον υπολογισμό των εν λόγω ιδιοτήτων χρησιμοποιήθηκε η μέθοδος του πεπερασμένου πεδίου. Τέλος πραγματοποιήθηκαν υπολογισμοί των ηλεκτρικών ιδιοτήτων αλληλεπίδρασης συστημάτων Η-(C≡C)n-H…Ηe για δυο συγκεκριμένες διαμορφώσεις ενώ για την αποφυγή του σφάλματος υπέρθεσης συνόλου βάσης χρησιμοποιήθηκε η υπερμοριακή προσέγγιση των Boys-Bernardi. / The purpose of the present doctoral dissertation is the calculation of the electric multipole moments (dipole up to hexadecapole) of acetylenic chains under the general formulas H-(C≡C)n-H, Χ-(C≡C)n-H and Χ-(C≡C)n-X, n=1–7, X=F, Cl, Br, I, CN, NC, the systematic study of the (hyper)polarizabilities of the non substituted acetylenic chains Η-(C≡C)n-H, n=3–7 and finally the calculation of interaction induced electric properties of systems of the general formula Η-(C≡C)n-H…Ηe, n=1– 7. In all cases considered the ab initio SCF and MP2 methods have been used along with the very popular DFT methods B3LYP, B3PW91 and mPW1PW91. For the electric multipole moment calculations the cc-pVDZ basis set has been used in all cases and special attention has been paid in the way the properties of interest change by changing the substituent at the ends of the acetylenic chains. For the electric (hyper)polarizability calculations on the non substituted acetylenic chains H-(C≡C)n- H minimally polarized basis sets have been used and comparison was made with the results obtained by using larger basis sets. In order to calculate the above mentioned properties the finite field method was applied. Finally, calculations were performed in order to calculate the interaction induced electric properties of the systems Η-(C≡C)n- H…Ηe for two particular configurations while in order to avoid the basis set superposition error the Boys-Bernardi counterpoise method has been applied.

Orientador: Pedro Antonio Muniz Vazquez / Tese (doutorado) - Universidade Estadual de Campinas, Instituto de Química / Made available in DSpace on 2018-08-23T04:27:58Z (GMT). No. of bitstreams: 1 Khan_Alamgir_D.pdf: 2306325 bytes, checksum: a39e71c04424c25645e57f5fe0ab453c (MD5) Previous issue date: 2013 / Resumo: Neste trabalho novas metodologias para cálculo das intensidades Raman absolutas de moléculas na fase gasosa foram desenvolvidas para uma série de moléculas pequenas, usando o método ab initio (CCSD) e a teoria do funcional de Densidade (DFT) (PBE0, LB94 e CAM-B3LYP) dentro da Teoria de Polarizabilidade de Placzek. A velocidade em cálculo junto com economia nos recursos computacionais foram estudadas usando dos conjuntos de bases polarizadas (potential efetivo de caroço) pSBKJC e pStuttgart desenvolvidos pelo nosso grupo através do procedimento "polarização eléctrica de Sadlej". Os resultados da metodolgia proposta em comparação com conjunto de bases Sadlej-pVTZ como referência, em níveis CCSD e DFT mostram acordos quantitativos nas propriedades e uma redução no tempo computacional. Na segunda parte deste trabalho, estas metodologias foram aplicadas para uma série de moléculas grandes de pesticidas organoclorados, ou seja; DDT e cinco análogos estruturas e de cinco pesticidas que contêm o grupo norborneno, utilizando métodos DFT (PBE0 e CAMB3LYP) para o cálculo das propriedades Raman. O conjunto de bases permitiram a redução o número de elétróns de 6 para 4 para carbono, 8 para 6 para oxigênio, 16 para 6 para o enxofre e 17 para 7 para o cloro. Assim, estas reduções de número de elétrons dá 50% de economia em recursos computacionais e tempo para os cálculos das propriedades ópticas das moléculas estudadas / Abstract: In this work new methodologies for calculating the absolute Raman intensities originating from gas phase molecules were developed for a set of small tests molecules, using ab initio quantum-mehancial (CCSD) and Density functional (PBE0, LB94 and CAMB3LYP functionals) methods within Placzek¿s Polarizability Theory. The speed-up in computation along with economy in the computational resources were studied using a newly polarized effective core potential basis set pSBKJC and pStuttgart developed by our group through Sadlej¿s electric polarization procedure. The results of the proposed methodology in comparison with Sadlej-pVTZ as reference basis set at CCSD and DFT levels show quite a good quantitative agreements in the properties with a valuable reduction in computational time and resources. In the second part of this work, the methodologies being assessed were applied for a series of large Organochlorinated pesticides ou seja, DDT and five structurally related pesticides and of five pesticides containing the Norbornene group, using DFT methods (PBE0 and CAMB3LYP functionals). The basis set allowed the reduction of the number of electrons from 6 to 4 for carbon, 8 to 6 for oxygen, 16 to 6 for sulfur and 17 to 7 for chlorine atoms. Thus, these reductions in electrons give more than 50% of savings in computer resources and time for the calculations of optical properties of reference molecules of environmental interests / Doutorado / Físico-Química / Doutor em Ciências

Proteins often carry an intrinsic electric dipole moment, which can interact with external electric fields and cause protein motion. Previous research has found that the orientation of small proteins in gas phase can be controlled in a static electric field. This effect is hoped to benefit applications such as single-particle imaging, and possibly other techniques involving proteins in electric fields. With the purpose of improving our understanding and modeling of protein orientation, this project investigated the scarcely explored quantum mechanical aspects of the process, namely the polarizability. Ground-state electronic structure simulations of three small model proteins, ubiquitin, Trp-cage and lysozyme, under the influence of electric fields were performed in vacuum. The electric dipole moments of the proteins were extracted from simulations with an applied electric field of strength 1 V/nm for varying angles, with respect to a body fixed reference frame. A Python program was written to analyze and visualize the results. The results point to a connection between the polarizability and the structure of the proteins, as well as size. Next a 3D rigid rotor model was developed using Mathematica in order to study the orientation dynamics classically in a simplified and time efficient way, with the possibility of including the previous quantum results. A comparison between a simulation of ubiquitin with and without polarizability concluded that the polarizability seems to have a damping effect on the orientation dynamics, at least for the initial conditions tested in this study. Further research is necessary to validate the model and perform statistical analysis of many simulations with varying initial conditions. / Proteiner bär ofta på ett inneboende elektriskt dipolmoment, som vid interaktion med externa elektriska fält och orsakar rörelse hos proteinerna. Tidigare studier har funnit att orienteringen av små proteiner i gasfas kan kontrolleras i ett statiskt elektriskt fält. Den effekten kan förhoppningsvis vara en fördel i tillämpningar såsom single-particle imaging, och eventuellt andra tekniker som innefattar proteiner i elektriska fält. I syftet att förbättra vår förståelse och modellering av protein-orientering, har detta projekt undersökt de föga utforskade kvantmekaniska aspekterna av processen, nämligen polariserbarheten. Kvant-baserade simuleringar av grundtillståndet av tre små proteiner, ubiquitin, Trp-cage och lysozym, under påverkan av elektriska fält utfördes i vakuum. Proteinernas elektriska dipolmoment extraherades från simuleringar med ett elektriskt fält med styrkan 1 V/nm för olika vinklar, med avseende på ett kroppsfixerat koordinatsystem. Ett Python-program skrevs för att analysera och visualisera resultaten. Resultaten tyder på att polariserbarheten beror på strukturen och storleken av proteinerna. Därefter utformades en stel-rotor-modell med hjälp av Mathematica för att studera prienteringen klassiskt på ett förenklat och tidseffektivt sätt, med möjligheten att inkludera de tidigare kvantmekaniska resultaten. En jämförelse mellan en simulering av ubiquitin med och utan polariserbarhet konstaterade att polariserbarheten verkar ha en dämpande effekt på orienteringen, åtminstone för begynnelsevillkoren som testades i denna studie. Vidare forskning krävs för att styrka modellen och utföra statistisk analys av många simuleringar med varierande begynnelsevillkor.

Clusters/nanoparticles are aggregates of a “small” number of building blocks, atoms or molecules, ranging from two up to millions of atoms. Two main groups of clusters have been studied using photoelectron spectroscopy based on synchrotron radiation. They are dry/wet alkali-halide clusters, including pure water clusters, and metal-based nanoparticles. For the dry alkali halide clusters, analysis of the data and theoretical modeling has allowed us insights into the local electronic properties at nanoscale: a change of polarizability of ions in the alkali-halide clusters due to the varying environment has been suggested. The study of the wet salt clusters shows that the alkali-halides are already solvated at the nanoscale reached by water clusters doped with salt vapor. The photoelectron angular distribution of water cluster shows lower anisotropy parameters as compared to the separate monomers. A model based on intracluster scattering has been built to partly explain the reduction. In the last part of the thesis, metal-based multi-component nanoparticles have been produced by self-assembly processes using reactive magnetron sputtering. Depending on the specific metal element, oxidation processes have been applied before or after the aggregation. Clearly radial distributions such as core-shell and “sandwich-like” structures have unambiguously determined by photoelectron spectroscopy.

Demonstration of ultrafast all-optical signal processing (AOSP) using silicon as the active material has been limited by large two-photon absorption loss and long lifetimes of the resulting free carriers. For AOSP at speeds in the terahertz, an order of magnitude faster than that the fastest current electronic counterpart, a class of π-conjugated organic molecules called polymethines provides a promising alternative to silicon as they possess large third-order nonlinearities, and ultrafast polarization response to an incident field. The challenge in the application of polymethines as active nonlinear optical materials for AOSP is in translating their promising molecular properties into bulk material properties. The large linear polarizability and charged nature of the polymethines molecules strongly promote aggregation and phase-separation in solid blends, offsetting their advantageous molecular optical properties. In this work, polymethines’ resistance to deleterious spontaneous symmetry breaking and aggregation was enhanced by substitutions of metal- and chalcogen- containing terminal groups, and rigid steric groups above and below the π-conjugated plane of polymethine chain. The resulting polymethines/amorphous polycarbonate (APC) blend films demonstrated an unprecedentedly high two-photon figure-of-merit, |Re(χ(3))/Im(χ(3))| and low linear loss. The optical quality of the polymethines/APC films was also improved by replacing the commonly-used alkyl ammonium counterions with more polarizable aryl phosphonium counterions with moderate ground state dipole moment. The resulting dye-polymer blend films showed an enhanced near-infrared transparency while its magnitude of the third-order susceptibility, |χ(3)|, showed a good agreement with that extrapolated from the molecular third-order polarizability, γ. For facile integration of these promising organic materials into SOH, the substrate surface was functionalized using silane coupling chemistry for the reduction of surface energy mismatch between the polymer films and the waveguide containing substrates. The optical and SEM micrographs showed vastly improved coverage and infiltration of the microfeatures. Furthermore, to enable the precise engineering of waveguide cross-sectional dimensions for single-mode propagation in the organic cladding, the dispersion curves of the polymethines/polymer blends were generated using prism coupling and ellipsometry. The combined efforts in the development of molecules and materials discussed in the thesis have culminated into a successful identification and optimization of the polymethines dyes and their polymer blends for imminent demonstrations of on-chip AOSP at terahertz speed.

19 Dec 2004. / Published through the Information Bridge: DOE Scientific and Technical Information. "IS-T 2009" Ivana Adamovic. 12/19/2004. Report is also available in paper and microfiche from NTIS.

CAPES - Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / CNPq - Conselho Nacional de Desenvolvimento Científico e Tecnológico / FAPEMIG - Fundação de Amparo a Pesquisa do Estado de Minas Gerais / A caracterização de materiais vítreos dopados tem sido uma área importante para o desenvolvimento de tecnologias fotônicas. Porém, com o desenvolvimento da nanociência e a descoberta das propriedades quânticas dos nanocristais, a quantidade de materiais vítreos a serem estudados aumentou de forma abrupta, o qual despertou um forte interesse da comunidade científica visando possíveis aplicações tecnológicas. O presente trabalho tem como objetivo investigar o índice de refração não linear da matriz vítrea a base de fosfato (P2O5 + AhO3 + Na2O + K2O) dopada com íons de neodímio e nanocristais de CdS. Destaca-se que a pesquisa corresponde à caracterização de uma matriz fosfata pouco conhecida na literatura, com dopantes de categorias distintas, sendo um Terra Rara e um nanocristal, nos quais apresentam picos de absorção próximos. Para a presente caracterização não linear, foi utilizada a técnica de Z-Scan, conhecido na literatura por sua simplicidade e precisão quando comparada com outras técnicas capazes de realizar a mesma medida. Medidas de absorção ótica e tempo de vida também foram feitas, pois fornecem parâmetros lineares para o cálculo das propriedades não lineares. Os resultados mostram que existe uma interação entre os dopantes, capaz de gerar uma variação nos parâmetros lineares e não lineares em estudo. / The characterization of doped glasses has been an important area for the development of photonic technologies. However, the development of nanoscience and the discovery of the quantic properties of nanocrystals, increased the number of researches in glass materials with interest in technological applications by the scientific community. This work aims to investigate the nonlinear refractive index of the phosphate glass matrix (P2O5 + Al2O3 + Na2O + K2O) doped with neodymium ions and CdS nanocrystals. This research characterizes a phosphate glass matrix, which is not well known in the literature with different dopants, in this case, rare earths and nanocrystals, which they show similar absorption peaks at ultraviolet. For a nonlinear optics characterization was used the Z-Scan technique, known to its simplicity and precision when compared to other techniques. Linear optical measurements were also made, such as optical absorption and lifetime, to calculate of non-linear optics properties. The results show there is an interaction between the dopants, capable of generating a variation in linear and nonlinear optical parameters under study. / Dissertação (Mestrado)

Nous avons étudié la spectroscopie et la dynamique d’excitation d’un système hybride constitué de molécules et de nanoparticules (NP) sur couche isolante, qui est aussi un catalyseur modèle (NP de Pd épitaxiées sur une couche mince de MgO sur Ag(100)). Nous avons mis en évidence le rôle de la forme et de la taille des NP ainsi que de l’épaisseur de la couche d’oxyde sur l’interaction entre NP et molécule de CO, par des expériences fondamentales capables de différentier les sites d’adsorption (spectroscopie laser vibrationnelle par somme de fréquences (SFG)). De plus, des expériences pompe-sonde nous ont permis de sonder la dynamique d’interaction des électrons excités dans les NP avec les molécules. Une analyse combinée par LEED et STM nous a permis de déterminer les meilleures conditions de croissance du film de MgO. Par la suite des NP de palladium ont été épitaxiées sur ce film avec une densité et une distribution de taille satisfaisantes. Les spectres SFG montre une forte dépendance de la fréquence de vibration avec la taille des NP et le taux de couverture en CO. Le modèle d’interaction dipolaire que nous avons développé met en évidence le fait que le déplacement de la fréquence de CO avec le taux de couverture et la taille des NP a deux causes : l’interaction dipolaire entre molécules d’une part, qui est modélisable, et d’autre part la variation de la liaison chimique molécule-substrat quand la couverture en adsorbats varie. Le modèle nous a permis de montrer que la polarisabilité vibrationnelle de CO varie d’environ 40 % dans notre gamme de taille de nanoparticule. La diminution de la force de la liaison chimique se traduit par la décroissance de la fréquence à couverture nulle avec la taille des NP. Ces variations vont dans le sens de la littérature : quand la taille des NP diminue, la densité d’états électroniques diminue, les liaisons Pd-Pd se contractent et l’énergie d’adsorption des molécules de CO diminue. L’excitation des électrons des NP et du substrat d’Ag se manifeste par une réponse spectroscopique et par la photodésorption de CO. On observe le découplage de l’excitation produite dans l’argent quand l’épaisseur de la couche d’oxyde dépasse quelques plans atomiques. On observe clairement un effet de taille sur l’efficacité de l’excitation électronique des NP sur les molécules de CO, qui diminue avec la taille des NP. Ceci montre que le confinement des électrons dans la particule a davantage pour effet d’augmenter la vitesse de relaxation électronique vers les phonons, que d’exciter plus efficacement les molécules adsorbées. Un modèle optique de double couche (NP/oxyde) sur un substrat d’argent et un modèle à trois températures (électrons, phonons et adsorbats) ont été développés dans le but d’interpréter quantitativement ces observations. Le modèle optique fait apparaître des variations très fortes de l’absorption par la couche de nanoparticules avec son épaisseur équivalente : les variations du coefficient de réflexion et l’effet des interférences multiples ne sont pas négligeables. Les résultats du modèle à trois températures montrent que la température électronique d’une couche continue est deux fois plus importante que celle des NP de taille finie. / We have studied the spectroscopy and excitation dynamics of a hybrid system consisting of molecules and nanoparticles (NPs) on insulating layer, which is also a model catalyst (Pd NPs grown on a thin layer of MgO on Ag(100)). We have highlighted the role of the shape and the NPs size as well as the thickness of the oxide layer in the interaction between NPs and CO molecules, by fundamental experiments allowing to differentiate the adsorption sites (Sum Frequency Generation (SFG)). In addition, pump-probe experiments allowed us to probe the dynamics of interaction between the photoexcited electrons bath in the NPs and the molecules. A combined study by LEED and STM allowed us to determine the growing conditions of MgO film. Subsequently palladium NPs were grown on this film with satisfying density and distribution size. The SFG spectra show a strong dependence of the vibrational frequency with the NPs size and the CO coverage. A dipole interaction model was developed showing that the CO frequency shift with the coverage and the NPs size has two causes: the dipolar interaction between molecules on the one hand, which is modeled, and on the other hand the variation of the molecule-substrate chemical bond when the adsorbate coverage varies. The model has allowed us to show that the vibrational polarizability of CO changes by 40 % in our range of NPs size. The decrease in the strength of the chemical bond results in the decrease of the frequency at zero coverage when the NPs size decreases. These variations are consistent with the literature: upon a decrease in the particle size, the electronic DOS decreases, the Pd-Pd bonds contract and the adsorption energy of CO molecules decreases. The electronic excitation of the NPs and the silver substrate manifested by the spectroscopic response and the CO photodesorption. We observed the decoupling of the electronic excitation produced in silver when the thickness of the oxide layer exceeds a few atomic planes. There is a clear size effect on the efficiency of electronic excitation of NPs on the CO molecules, which decreases as the NPs size decreases. This shows that the effect of electrons confinement in the particle rather consists in an increase in the relaxation rate of electrons to phonons, than in a more efficient excitation of the adsorbed molecules. A double-layer optical model (NP/oxide) on a silver substrate and a three-temperature model (electrons, phonons and adsorbates) have been developed to quantitatively interpret these observations. The optical model results show a very strong variation of the absorption intensity by the layer with its equivalent thickness: variation of the reflection and the effect of multiple interference are not negligible. The three temperatures model results show that the electronic temperature of a continuous layer is two times more important than in the case of finite size NPs.