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Pathway and kinetic analysis on the iso-propyl radical + O{sub 2} reaction system

Description: We analyze the isopropyl + 02 reaction system using thermochemical Transition State Theory (TST), molecular thermodynamic properties, analysis (quantum RRK) for k(E) and modified strong collision analyze Cyclic transition states for both hydrogen transfer and concerted propylene from isopropylperoxy are calculated using semi-empirical theory in addition to transition states for H02 elimination from hydroperoxy-isopropyl. Computed rate constants are compared to constant measurements of for isopropyl + H02.
Date: April 7, 1997
Creator: Bozzelli, J. W. & Pitz, W. J.
Partner: UNT Libraries Government Documents Department

Beyond transition state theory: Rigorous quantum approaches for determining chemical reaction rates

Description: Transition state theory (TST) has historically been the most important and widely used theoretical approach for describing the rates of chemical reactions, and for qualitative pictures and order-of-magnitude estimates one does not expect this situation to change. However a rigorous, quantitative treatment of chemical reaction rates must go beyond TST. A rigorous description, for example, must be based on a quantum mechanical description of the molecular system, but the fundamental assumption on which TST is based - namely that the molecular dynamics is {open_quotes}direct,{close_quotes} i.e., that no trajectories re-cross a dividing surface which separates reactants and products (vide infra) - is couched inherently in the language of classical mechanics. There is no unambiguous way to quantize TST, for the various ways of trying to do so invariably require one to introduce additional assumptions about the reaction dynamics. As one tries to eliminate these {open_quotes}additional assumptions{close_quotes} one is driven ultimately to an exact quantum treatment of the reaction dynamics which is then no longer a transition state theory (i.e., approximation) but simply an exact formulation. It is such exact approaches, those without inherent approximations, that are the subject of this chapter.
Date: January 1, 1995
Creator: Miller, W.H.
Partner: UNT Libraries Government Documents Department

Quartz Channel Fabrication for Electrokinetically Driven Separations

Description: For well resolved electrokinetic separation, we L tilize crystalline quartz to micromachine a uniformly packe Q&iKLmnel. Packing features are posts 5 Vm on a side with:} pm spacing and etched 42 Vm deep. In addition to anisotropic wet etch characteristics for micromachining, quartz propmties are compatible with chemical soiutioits, ekctrokinetic high voltage operation, and stationary phase film depositions. To seal these channels, we employ a room temperature silicon-oxynhride deposition to forma membrane, that is subsequently coated for mechanical stability. Using this technique, particulate issues and global warp, that make large area wafer bon ding methods difficult, are avoided, and a room temperature process, in contrast to high temperature bonding techniques, accommodate preprocessing of metal films for electrical interconnect. After sealing channels, a number of macro-assembly steps are required to attach a micro-optical detection system and fluid interconnects. Keywords: microcharmel, integrated channel, micromachined channel, packed channel, electrokinetic channel, eleetrophoretic channel
Date: December 1, 1998
Creator: Arnold, D.W.; Ashby, C.I.H.; Bailey, C.G.; Kravitz, S.H., Warren, M.E. & Matzke, C.M.
Partner: UNT Libraries Government Documents Department

Pathway and kinetic analysis on the propyl radical + 02 reaction system

Description: In this study of the reaction of alkyl radicals with molecular oxygen, we analyze the propyl + 02 reaction system using thermochemical kinetics, Transition State Theory (TST), molecular thermodynamic properties, quantum Kassel analysis (quantum RRK) for k(E) and modified strong collision analysis for fall off. Cyclic transition states for both hydrogen transfer and the H02 concerted elimination from propylperoxy are calculated using semi-empirical (MOPAC PM3) calculations [8] in addition to transition states for H02 elimination and epoxide formation from hydroperoxy-isopropyl. Computed rate constants for propyl + 02 are compared to the values of Gulati and Walker who measured the rate constants at 50 torr and over a temperature range of 653 to 773 K. Computed rate constants are also used in a detailed chemical kinetic mechanism and compared to the n- propyl + 02 data of Slagle. They measured the rate of disappearance of n-propyl by reaction with 02 over a temperature range of 297 to 635 K and a pressure range of 0.4 to 7 Torr, as well as the fall off data of the Kaiser and Wallington.
Date: May 1, 1997
Creator: Bozzelli, J.W. & Pitz, W.J.
Partner: UNT Libraries Government Documents Department

Chemical Kinetics for Modeling Silicon Epitaxy from Chlorosilanes

Description: A reaction mechanism has been developed that describes the gas-phas 0971 and surface reactions involved in the chemical vapor deposition of Si from chlorosilanes. Good agreement with deposition rate data from a single wafer reactor with no wafer rotation has been attained over a range of gas mixtures, total flow rates, and reactor temperatures.
Date: November 24, 1998
Creator: Balakrishna, A.; Chacin, J.M.; Comita, P.B.; Haas, B.; Ho, P. & Thilderkvist, A.
Partner: UNT Libraries Government Documents Department

Recent advances in the measurement of high temperature bimolecular rate constants

Description: Recent advances in the measurement of high temperature reaction rate constants are discussed. The studies carried out by shock tube methods are particularly considered because these results are important not only in theoretical chemical kinetics but also in practical applications. The work on 5 chemical reactions are reviewed in detail. These are: D + H{sub 2}, Cl + H{sub 2}, H + O{sub 2}, CH{sub 3} + CH{sub 3}, and H + NO{sub 2}.
Date: July 1, 1995
Creator: Michael, J.V.
Partner: UNT Libraries Government Documents Department

A Survey of the Rates and Products of Short-Term Photosynthesis inPlants of 9 Phyla

Description: The conclusions of this paper are: (1) Short-term photosynthetic experiments using C{sup 14}O{sub 2} and paper chromatography were performed with 27 different plants representing nine phyla: Schizophyta (Schizophyceae), Euglenophyta, Chlorophyta, Charophyta, Chrysophyta, Rhodophyta, Bryophyta, Pteridophyta, and Spermatophyta. (2) There is a remarkable uniformity in the types of ethanol-soluble compounds which became radioactive in the entire group of plants used. The amounts of the different compounds varied considerably percentage-wise among the various plants as would be expected because of their inherent metabolic differences and the variations in their physiological states induced by experimental conditions. (3) Sucrose became radioactive in very different amounts in two major groupings of plants: (a) those containing only photosynthetic tissue and (b) those containing non-photosynthetic tissue as well. The amount of radioactive sucrose in the former group was much lower than that in the latter. (4) An unidentified compound became radioactive in appreciable amounts in two of the blue-green algae, but was radioactive in very small amounts or not visible at all on the chromatograms of all other plants.
Date: May 1, 1954
Creator: Calvin, M.; Norris, R.E. & Norris, Louisa
Partner: UNT Libraries Government Documents Department

Diesel combustion: an integrated view combining laser diagnostics, chemical kinetics, and empirical validation

Description: This paper proposes a structure for the diesel combustion process based on a combination of previously published and new results. Processes are analyzed with proven chemical kinetic models and validated with data from production-like direct injection diesel engines. The analysis provides new insight into the ignition and particulate formation processes, which combined with laser diagnostics, delineates the two-stage nature of combustion in diesel engines. Data are presented to quantify events occurring during the ignition and initial combustion processes that form soot precursors. A framework is also proposed for understanding the heat release and emission formation processes.
Date: February 1, 1999
Creator: Akinyami, O C; Dec, J E; Durrett, R P; Flynn, P F; Hunter, G L; Loye, A O et al.
Partner: UNT Libraries Government Documents Department

Free-radical kinetics of coal liquefaction

Description: A rate expression with first- and second-order terms in the concentration of extractable compounds in solid coal particles is derived from a fundamental free-radical mechanism. The expression was suggested empirically by prior experiments for coal liquefaction in the presence of a hydrogen-donor solvent. Radical reactions are considered to occur in both coal and in solvent. The long-chain approximation justifies the neglect of initiation, hydrogen abstraction, and termination rates as quantitatively insignificant relative to propagation reaction rates.
Date: July 16, 1994
Creator: Wang, M.; Smith, J.M. & McCoy, B.J.
Partner: UNT Libraries Government Documents Department

Thermal Decomposition Characteristics of Orthorhombic Ammonium Perchlorate (o-AP)

Description: Preliminary STMBMS and SEM results of the thermal decomposition of AP in the orthorhombic phase are presented. The overall decomposition is shown to be complex and controlled by both physical and chemical processes. The data show that the physical and chemical processes can be probed and characterized utilizing SEM and STMBMS. The overall decomposition is characterized by three distinguishing features: an induction period, and accelerator period and a deceleratory period. The major decomposition event occurs in the subsurface of the AP particles and propagates towards the center of the particle with time. The amount of total decomposition is dependent upon particle size and increases from 23% for {approximately}50{micro}m-diameter AP to 33% for {approximately}200{micro}m-diameter AP. A conceptual model of the physical processes is presented. Insight into the chemical processes is provided by the gas formation rates that are measured for the gaseous products. To our knowledge, this is the first presentation of data showing that the chemical and physical decomposition processes can be identified from one another, probed and characterized at the level that is required to better understand the thermal decomposition behavior of AP. Future work is planned with the goal of obtaining data that can be used to develop a mathematical description for the thermal decomposition of o-AP.
Date: March 1, 1999
Creator: Behrens, R. & Minier, L.
Partner: UNT Libraries Government Documents Department

First-principles study of high explosive decomposition energetics

Description: The mechanism of the gas phase unimolecular decomposition of hexahydro-1,3,5,- trinitro- 1,3,5,-triazine (RDX) has been investigated using first principles gradient corrected density functional theory. Our results show that the dominant reaction channel is the N-NO* bond rupture, which has a barrier of 34.2 kcal/mol at the B- PW9 l/cc-pVDZ level and is 18.3 kcal/mol lower than that of the concerted ring fission to three methylenenitramine molecules. In addition, we have carried out a systematic study of homolytic bond dissociation energies of 14 other high explosives at the B-PW91/D95V level. We find that the correlation between the weakest bond strength and high explosive sensitivity is strong
Date: August 21, 1998
Creator: Wu, C J
Partner: UNT Libraries Government Documents Department

Origin of the Time-Dependence of Wet Oxidation of AlGaAs

Description: The time-dependence of the wet oxidation of high-Al-content AlGaAs can be either linear, indicating reaction-rate limitation, or parabolic, indicating diffusion-limited rates. The transition from linear to parabolic time dependence can be explained by the increased rate of the formation of intermediate As{sub 2}O{sub 3} vs. its reduction to elemental As. A steadily increasing thickness of the As{sub 2}O{sub 3}-containing region at the oxidation front will shift the process from the linear to the parabolic regime. This shift from reaction-rate-limited (linear) to diffusion-limited (parabolic) time dependence is favored by increasing temperature or increasing Al mole fraction.
Date: February 15, 1999
Creator: Allerman, A.A.; Ashby, C.I.H.; Bridges, M.M.; Hammons, B.E. & Hou, H.Q.
Partner: UNT Libraries Government Documents Department

Degradation kinetics of polymers in solution: Time-dependence of molecular weight distributions. [Quarterly report, January--March 1996]

Description: Polymer degradation occurs when polymer chains are broken under the influence of thermal, mechanical, or chemical energy. Chain-end depolymerization and random- and midpoint-chain scission are mechanisms that have been observed in liquid-phase polymer degradation. Here we develop mathematical models, unified by continuous-mixture kinetics, to show how these different mechanisms affect polymer degradation in solution. Rate expressions for the fragmentation of molecular-weight distributions (MWDs) govern the evolution of the MWDs. The governing integro-differential equations can be solved analytically for realistic conditions. Moment analysis for first-order continuous kinetics shows the temporal behavior of MWDs. Chain-end depolymerization yields monomer product and polymer molecular-weight moments that vary linearly with time. In contrast, random- and midpoint-chain scission models display exponential time behavior. The mathematical results reasonably portray experimental observations for polymer degradation. This approach, based on the time evolution of continuous distributions of chain length or molecular weight, provides a framework for interpreting several types of polymer degradation processes.
Date: February 27, 1996
Creator: McCoy, B.J. & Madras, G.
Partner: UNT Libraries Government Documents Department

Competitive ion kinetics in direct mass spectrometric organic speciation. 1993 Progress report

Description: The following joint projects are either in progress, or have been completed. (1) Southern Illinois University, Prof. S. Scheiner--Combined experimental-theoretical study of the thermochemistry of protonation, complexation, and hydration of di- and polyfunctional ethers. (2) Eastern illinois University, Prof. C. Deakyne--Essentially the same framework as above. The focus here was to determine whether C or N lone pair electrons were more effective in forming ionic hydrogen bonds. (3) Virginia Commonwealth University-Prof. S. El-Shall--The author put the wrap on a joint thermochemical (NIST) and beam expansion study (VCU) which probed structures and stabilities of methanol clusters incorporating either CH{sub 3}CN or (CH{sub 3}){sub 3}N. MeCN and TMA were chosen because of their widely differing proton affinities (PA`s) and the fact that they form single H-bonds (i.e., complex intraclusters involving multiple bonding are unlikely). (4) University of Maryland-Baltimore County-Prof. J. Liebman and the Phillips Laboratory Supercomputer Center, Kirtland Air Force Base, NM-A. Fant--One of the most perplexing problems among physical organic chemists has involved the site of protonation of a class of molecules referred to as quinones and, in particular, the symmetric member, para-benzoquinone, C{sub 6}H{sub 4} (=O{sub 2}), designated below as PBQ. Possible protonation sites either the ring or carbonyl function.
Date: December 31, 1993
Creator: Sieck, L.W.
Partner: UNT Libraries Government Documents Department

Simplified models of growth, defect formation, and thermal conductivity in diamond chemical vapor deposition

Description: A simplified surface reaction mechanism is presented for the CVD of diamond thin films. The mechanism also accounts for formation of point defects in the diamond lattice, an alternate, undesirable reaction pathway. Both methyl radicals and atomic C are considered as growth precursors. While not rigorous in all details, the mechanism is useful in describing the CVD diamond process over a wide range of reaction conditions. It should find utility in reactor modeling studies, for example in optimizing diamond growth rate while minimizing defect formation. This report also presents a simple model relating the diamond point-defect density to the thermal conductivity of the material.
Date: April 1, 1996
Creator: Coltrin, M.E. & Dandy, D.S.
Partner: UNT Libraries Government Documents Department

Experimental and theoretical investigation of the product channels of the O + CH{sub 3} reaction

Description: The product channels of the O({sup 3}P)+CH{sub 3} reaction was investigated. In the experimental part, the branching fraction for formaldehyde production (O+CH{sub 3}{r_arrow}H{sub 2}CO+H) was measured at room temperature in a tubular flow reactor coupled to a photoionization mass spectrometer. The reactants (CH{sub 3} and O) were generated homogeneously in the reactor by simultaneous {ital in}{ital situ} 193-nm photolysis of acetone and SO{sub 2}. Formaldehyde yield relative to the methyl radicals consumed (branching fraction) was determined to be 1.0{+-}0.15. In the theoretical part, calculations of the energetics of possible decomposition pathways of the energy-rich methoxy radical initially formed in the O+CH{sub 3} reaction indicate that the dominant channel for decomposition is C-H bond cleavage leading to atomic hydrogen and formaldehyde. A possible, minor, secondary channel is hydrogen migration, followed by O-H bond cleavage, leading to the same final products. No energetically competitive pathways leading to H{sub 2}, HCO, HOC, or CO could be found.
Date: May 1, 1994
Creator: Slagle, I.R.; Kalinovski, I.J.; Gutman, D. & Harding, L.B.
Partner: UNT Libraries Government Documents Department