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  Partner: UNT Libraries
 Department: Department of Chemistry
 Decade: 2010-2019
 Language: English
 Collection: UNT Theses and Dissertations
Accuracy and Efficiency in Computational Chemistry: The Correlation Consistent Composite Approach

Accuracy and Efficiency in Computational Chemistry: The Correlation Consistent Composite Approach

Date: August 2011
Creator: Wilson, Brent R.
Description: One of the central concerns of computational chemistry is that of efficiency (i.e. the development of methodologies which will yield increased accuracy of prediction without requiring additional computational resources – RAM, disk space, computing time). Though the equations of quantum mechanics are known, the solutions to these equations often require a great deal of computing power. This dissertation primarily concerns the theme of improved computational efficiency (i.e. the achievement of greater accuracy with reduced computational cost). Improvements in the efficiency of computational chemistry are explored first in terms of the correlation consistent composite approach (ccCA). The ccCA methodology was modified and this enhanced ccCA methodology was tested against the diverse G3/05 set of 454 energetic properties. As computational efficiency improves, molecules of increasing size may be studied and this dissertation explored the issues (differential correlation and size extensivity effects) associated with obtaining chemically accurate (within 1 kcal mol-1) enthalpies of formation for hydrocarbon molecules of escalating size. Two applied projects are also described; these projects concerned the theoretical prediction of a novel rare gas compound, FKrOH, and the mechanism of human glutathione synthetase’s (hGS) negative cooperativity. The final work examined the prospect for the parameterization of the modified embedded atom ...
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Advancements in Instrumentation for Fourier Transform Microwave Spectroscopy

Advancements in Instrumentation for Fourier Transform Microwave Spectroscopy

Date: August 2011
Creator: Dewberry, Christopher Thomas
Description: The efforts of my research have led to the successful construction of several instruments that have helped expand the field of microwave spectroscopy. The classic Balle-Flygare spectrometer has been modified to include two different sets of antenna to operate in the frequency ranges 6-18 GHz and 18-26 GHz, allowing it to function for a large range without having to break vacuum. This modified FTMW instrument houses two low noise amplifiers in the vacuum chamber to allow for the LNAs to be as close to the antenna as physically possible, improving sensitivity. A new innovative Balle-Flygare type spectrometer, the efficient low frequency FTMW, was conceived and built to operate at frequencies as low as 500 MHz through the use of highly curved mirrors. This is new for FTMW techniques that normally operate at 4 GHz or higher with only a few exceptions around 2 GHz. The chirped pulse FTMW spectrometer uses horn antennas to observe spectra that span 2 GHz versus the standard 1 MHz of a cavity technique. This instrument decreases the amount of time to obtain a large spectral region of relative correct intensity molecular transitions. A Nd:YAG laser ablation apparatus was attached to the classic Balle-Flygare and chirped ...
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Affordances of Instrumentation in General Chemistry Laboratories

Affordances of Instrumentation in General Chemistry Laboratories

Date: August 2010
Creator: Sherman, Kristin Mary Daniels
Description: The purpose of this study is to find out what students in the first chemistry course at the undergraduate level (general chemistry for science majors) know about the affordances of instrumentation used in the general chemistry laboratory and how their knowledge develops over time. Overall, students see the PASCO™ system as a useful and accurate measuring tool for general chemistry labs. They see the probeware as easy to use, portable, and able to interact with computers. Students find that the PASCO™ probeware system is useful in their general chemistry labs, more advanced chemistry labs, and in other science classes, and can be used in a variety of labs done in general chemistry. Students learn the affordances of the probeware through the lab manual, the laboratory teaching assistant, by trial and error, and from each other. The use of probeware systems provides lab instructors the opportunity to focus on the concepts illustrated by experiments and the opportunity to spend time discussing the results. In order to teach effectively, the instructor must know the correct name of the components involved, how to assemble and disassemble it correctly, how to troubleshoot the software, and must be able to replace broken or missing components ...
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Boron Nitride by Atomic Layer Deposition: A Template for Graphene Growth

Boron Nitride by Atomic Layer Deposition: A Template for Graphene Growth

Date: August 2011
Creator: Zhou, Mi
Description: The growth of single and multilayer BN films on several substrates was investigated. A typical atomic layer deposition (ALD) process was demonstrated on Si(111) substrate with a growth rate of 1.1 Å/cycle which showed good agreement with the literature value and a near stoichiometric B/N ratio. Boron nitride films were also deposited by ALD on Cu poly crystal and Cu(111) single crystal substrates for the first time, and a growth rate of ~1ML/ALD cycle was obtained with a B/N ratio of ~2. The realization of a h-BN/Cu heterojunction was the first step towards a graphene/h-BN/Cu structure which has potential application in gateable interconnects.
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Characterization of Novel Solvents and Absorbents for Chemical Separations

Characterization of Novel Solvents and Absorbents for Chemical Separations

Date: May 2011
Creator: Grubbs, Laura Michelle Sprunger
Description: Predictive methods have been employed to characterize chemical separation mediums including solvents and absorbents. These studies included creating Abraham solvation parameter models for room-temperature ionic liquids (RTILs) utilizing novel ion-specific and group contribution methodologies, polydimethyl siloxane (PDMS) utilizing standard methodology, and the micelles cetyltrimethylammonium bromide (CTAB) and sodium dodecylsulfate (SDS) utilizing a combined experimental setup methodology with indicator variables. These predictive models allows for the characterization of both standard and new chemicals for use in chemical separations including gas chromatography (GC), solid phase microextraction (SPME), and micellar electrokinetic chromatography (MEKC). Gas-to-RTIL and water-to-RTIL predictive models were created with a standard deviation of 0.112 and 0.139 log units, respectively, for the ion-specific model and with a standard deviation of 0.155 and 0.177 log units, respectively, for the group contribution fragment method. Enthalpy of solvation for solutes dissolved into ionic liquids predictive models were created with ion-specific coefficients to within standard deviations of 1.7 kJ/mol. These models allow for the characterization of studied ionic liquids as well as prediction of solute-solvent properties of previously unstudied ionic liquids. Predictive models were created for the logarithm of solute's gas-to-fiber sorption and water-to-fiber sorption coefficient for polydimethyl siloxane for wet and dry conditions. These models ...
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Chirped-Pulse Fourier Transform Microwave Spectroscopy of Fluoroiodoacetonitrile and Chloropentafluoroacetone

Chirped-Pulse Fourier Transform Microwave Spectroscopy of Fluoroiodoacetonitrile and Chloropentafluoroacetone

Date: December 2010
Creator: Kadiwar, Gautam
Description: This work focuses on finding the complete iodine and nitrogen nuclear electric quadrupole coupling tensors for fluoroiodoacetonitrile using chirped-pulse Fourier transform microwave spectroscopy. Fluoroiodoacetonitrile contains two hyperfine nuclei, iodine (I=5/2) and nitrogen (I=1) and the spectra were observed with great resolution. A total of 499 transitions were observed for this molecule. The a, b and c rotational constants were obtained. A study of chloropentafluoroacetone was also done using chirped-pulse Fourier transform microwave spectroscopy. The two chlorine isotopes for this molecule, Cl-35 and Cl-37 were observed and 326 and 170 transitions were recorded, respectively.
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Computational Investigation of Molecular Optoelectronic and Biological Systems

Computational Investigation of Molecular Optoelectronic and Biological Systems

Date: August 2011
Creator: Tekarli, Sammer M.
Description: The scope of work in this dissertation has comprised several major investigations on applications and theoretical studies of ab initio quantum mechanics and density functional theory where those techniques were applied to the following: (i) investigation of the performance of density functionals for the computations of molecular properties of 3d transition metal containing systems; (ii) guidance for experimental groups for rational design of macrometallocyclic multinuclear complexes with superior π-acidity and π-basicity that are most suitable for p- and n-type semiconductors of metal-organic molecules and nanomaterials; (iii) investigation of the metallo-aromaticity of multi-nuclear metal complexes; (iv) investigation of the kinetics and thermodynamics of copper-mediated nitrene insertion into C-H and H-H bond; and (v) accurate computations of dissociation energies of hydrogen-bonded DNA duplex moieties utilizing the resolution of identity correlation consistent composite approach (RI-ccCA).
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Computational Studies of Inorganic Systems with a Multiscale Modeling Approach: From Atomistic to Continuum Scale

Computational Studies of Inorganic Systems with a Multiscale Modeling Approach: From Atomistic to Continuum Scale

Date: August 2013
Creator: Olatunji-Ojo, Olayinka A.
Description: Multiscale modeling is an effective tool for integrating different computational methods, creating a way of modeling diverse chemical and physical phenomena. Presented are studies on a variety of chemical problems at different computational scales and also the combination of different computational methods to study a single phenomenon. The methods used encompass density functional theory (DFT), molecular dynamics (MD) simulations and finite element analysis (FEA). The DFT studies were conducted both on the molecular level and using plane-wave methods. The particular topics studied using DFT are the rational catalyst design of complexes for C—H bond activation, oxidation of nickel surfaces and the calculation of interaction properties of carbon dioxide containing systems directed towards carbon dioxide sequestration studies. Second and third row (typically precious metals) transition metal complexes are known to possess certain electronic features that define their structure and reactivity, and which are usually not observed in their first-row (base metal) congeners. Can these electronic features be conferred onto first-row transition metals with the aid of non-innocent and/or very high-field ligands? Using DFT, the impact of these electronic features upon methane C—H bond activation was modeled using the dipyridylazaallyl (smif) supporting ligand for late, first-row transition metal (M) imide, oxo and ...
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Computational Study of Small Molecule Activation via Low-Coordinate Late First-Row Transition Metal Complexes

Computational Study of Small Molecule Activation via Low-Coordinate Late First-Row Transition Metal Complexes

Date: May 2010
Creator: Pierpont, Aaron
Description: Methane and dinitrogen are abundant precursors to numerous valuable chemicals such as methanol and ammonia, respectively. However, given the robustness of these substrates, catalytically circumventing the high temperatures and pressures required for such transformations has been a challenging task for chemists. In this work, computational studies of various transition metal catalysts for methane C-H activation and N2 activation have been carried out. For methane C-H activation, catalysts of the form LnM=E are studied, where Ln is the supporting ligand (dihydrophosphinoethane or β-diketiminate), E the activating ligand (O, NCH3, NCF3) at which C-H activation takes place, and M the late transition metal (Fe,Co,Ni,Cu). A hydrogen atom abstraction (HAA) / radical rebound (RR) mechanism is assumed for methane functionalization (CH4 à CH3EH). Since the best energetics are found for (β-diket)Ni=O and (β-diket)Cu=O catalysts, with or without CF3 substituents around the supporting ligand periphery, complete methane-to-methanol cycles were studied for such systems, for which N2O was used as oxygen atom transfer (OAT) reagent. Both monometallic and bimetallic OAT pathways are addressed. Monometallic Fe-N2 complexes of various supporting ligands (LnFe-N2) are studied at the beginning of the N2 activation chapter, where the effect of ligand on N2 activation in end-on vs. side-on N2 isomers ...
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Cu Electrodeposition on Ru-Ta and Corrosion of Plasma Treated Cu in Post Etch Cleaning Solution

Cu Electrodeposition on Ru-Ta and Corrosion of Plasma Treated Cu in Post Etch Cleaning Solution

Date: August 2011
Creator: Sundararaju Meenakshiah Pillai, Karthikeyan
Description: In this work, the possibility of Cu electrodeposition on Ru-Ta alloy thin films is explored. Ru and Ta were sputter deposited on Si substrate with different composition verified by RBS. Four point probe, XRD, TEM and AFM were used to study the properties of Ru-Ta thin films such as sheet resistance, crystallinity, grain size, etc. Cyclic voltammetry is used to study the Cu electrodeposition characteristics on Ru-Ta after various surface pretreatments. The results provide insights on the removal of Ta oxide such that it enables better Cu nucleation and adhesion. Bimetallic corrosion of Cu on modified Ru-Ta surface was studied in CMP related chemicals. In Cu interconnect fabrication process, the making of trenches and vias on low-k dielectric films involves the application of fluorocarbon plasma etch gases. Cu microdots deposited on Ru and Ta substrate were treated by fluorocarbon plasma etch gases such as CF4, CF4+O2, CH2F2, C4F8 and SF6 and investigated by using x-ray photoelectron spectroscopy, contact angle measurement and electrochemical techniques. Micropattern corrosion screening technique was used to measure the corrosion rate of plasma treated Cu. XPS results revealed different surface chemistry on Cu after treating with plasma etching. The fluorine/carbon ratio of the etching gases results in ...
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