1,176 Matching Results

Search Results

Advanced search parameters have been applied.

Stabilization of Free Radicals at Low Temperatures: Summary of the NBS Program

Description: From Forward: "Although the first paper in this volume describes the general aspects of the technical management of the program, it is important to emphasize that much of success and productivity of this program stemmed from the sympathetic understanding of its basic viewpoint by both the Department of Defense and the National Bureau of Standards."
Date: August 1, 1960
Creator: Bass, Arnold M. & Broida, H. P.
Partner: UNT Libraries Government Documents Department

Proceedings of the International Symposium on Free Radicals: 1985

Description: Abstract: This publication contains papers presented at the Seventeenth International Symposium on Free Radicals, held at Snow Mountain Ranch in Granby, Colorado, on August 18-23, 1985. The Symposium was attended by 147 people, representing industry, government, and academia, from 18 countries. A total of 67 papers appear in written form in this document.
Date: April 1986
Creator: Evenson, Kenneth M.
Partner: UNT Libraries Government Documents Department

Reaction of hydroxyl radicals with trichloroethylene: Evidence for chlorine elimination channels at elevated temperatures

Description: Article on the reaction of hydroxyl radicals with trichloroethylene and evidence for chlorine elimination channels at elevated temperatures.
Date: 2000
Creator: Tichenor, LeAnn B.; Lozada-Ruiz, Alexei I.; Yamada, Takahim; El-Sinawi, Abdulaziz; Taylor, Philip H.; Peng, Jingping et al.
Partner: UNT College of Arts and Sciences

Effect of Free Methyl Radicals on Slow Oxidation of Propane and Ethane

Description: Memorandum presenting a study of the effect of free methyl radicals on the slow oxidation of both ethane and propane by means of a photochemical decomposition reaction in a static system. The introduction of methyl radicals into a mixture of propane and oxygen or ethane and oxygen substantially lowered the initiation temperature of the combustion of the hydrocarbon.
Date: August 28, 1952
Creator: McDonald, Glen E. & Schalla, Rose L.
Partner: UNT Libraries Government Documents Department

Comparison of fast 3D simulation and actinic inspection for EUV masks with buries defects

Description: Aerial images for isolated defects and the interactions of defects with features are compared between the Actinic Inspection Tool (AIT) at Lawrence Berkeley National Laboratory (LBNL) and the fast EUV simulation program RADICAL. Comparisons between AIT images from August 2007 and RADICAL simulations are used to extract aberrations. At this time astigmatism was the dominant aberration with a value of 0.55 waves RMS. Significant improvements in the imaging performance of the AIT were made between August 2007 and December 2008. A good match will be shown between the most recent AIT images and RADICAL simulations without aberrations. These comparisons will demonstrate that a large defect, in this case 7nm tall on the surface, is still printable even if it is centered under the absorber line. These comparisons also suggest that the minimum defect size is between 1.5nm and 0.8nm surface height because a 1.5nm defect was printable but a 0.8nm was not. Finally, the image of a buried defect near an absorber line through focus will demonstrate an inversion in the effect of the defect from a protrusion of the dark line into the space to a protrusion of the space into the line.
Date: February 23, 2009
Creator: Clifford, C. H.; Wiraatmadja, S.; Chan, T. T.; Neureuther, A. R.; Goldberg, K. A.; Mochi, I. et al.
Partner: UNT Libraries Government Documents Department

Reaction of Phenyl Radical with O2: Thermodynamic Properties, Important Reaction Paths and Kinetics

Description: The Phenyl + O{sub 2} association results in a chemically activated phenyl-peroxy radical which can dissociate to phenoxy radical + O, undergo intramolecular addition of the peroxy radical to several unsaturated carbon sites or react back to phenyl + O{sub 2}. The intramolecular addition channels further react through several paths to ring opening (unsaturated + carbonyl moieties) as well as cyclopentadieny radical + CO{sub 2}. Enthalpy ({Delta}H{sub f(298)}{sup o}), Entropy (S{sub 298}), and heat capacities Cp(T) for species in the decomposition of the ring are evaluated using density functional and ab initio calculations and by comparisons to vinyl + O{sub 2} data of Mebel et al, and phenyl + O{sub 2} data of Hadad et al. Isodesmic reaction analysis is used to estimate enthalpy values of the intermediates and well depths of the adducts. High Pressure limit kinetic parameters are obtained from the calculation results using canonical Transition State Theory. Quantum RRK analysis is utilized to obtain k(E) and modified strong collision or master equation analysis is used for evaluation of pressure fall-off in this complex bimolecular, chemical activation, reaction system. Uncertainty in key barriers is discussed, resulting variations in important reaction product ratios are illustrated, and changes in these branching ratios are evaluated with a detailed reaction mechanism.
Date: April 12, 2001
Creator: Bozzelli, J; Sebbar, N; Pitz, W & Bockhorn, H
Partner: UNT Libraries Government Documents Department

Experimental and theoretical studies of solvation of ions

Description: Solvents determine the outcome of many industrial chemical reactions. Sometimes small changes in the properties of the solvent system can have dramatic consequences on the economics of these processes, and a broad array of empirical analyses have been performed to evaluate solvent effects on chemical processes. Chemists at Argonne National Laboratory have adopted a very direct approach and are measuring the actual rates of salvation of large organic anions in different solvents for the first time. Chuck Jonah and Yi Lin used the Argonne linac to create the anions in an unsolvated state, and then studied the manner in which they interacted with surrounding molecules. They showed that anion salvation occurs at a much faster rate than had been predicted, and they provided a theoretical understanding of the way in which the reaction rates intimately depend upon the chemical structures of the solvents. These experiments, which provide new insight into this important aspect of chemistry, were carried out using the Argonne picosecond linac and the stroboscopic pulse radiolysis system.
Date: March 1996
Creator: Jonah, C. D. & Lin, Yi
Partner: UNT Libraries Government Documents Department

The Consequences of Surface Confinement on Free Radical Chemistry

Description: Mass transport limitations impact the thermochemical processing of fossil and renewable energy resources, which involves the breakdown of cross-linked, macromolecular networks. To Investigate the molecular level details of the consequences of molecular confinement on high temperature (275-500°C) free-radical reaction pathways, we have been examining the pyrolysis of model compounds attached to the surface of non-porous silica nanoparticles through a thermally robust Si-O-C<sub>aryl</sub>, tetha. Pyrolysis of silica-immobilized diphenylalkanes and related ethers have been studied in detail and compared with the corresponding behavior in fluid phases. The diffusional constraints can lead to reduced rates of radical termination on the surface, and enhancement of neophyl-like rearrangements, cyclization-dehydrogenation pathways, and <i>ipso-</i> aromatic substitutions. Furthermore, studies of two-component surfaces have revealed the importance of a radical relay mechanism involving rapid serial hydrogen transfer steps resulting from the molecular pre-organization on the low fractal dimension silica surface. Key findings are reviewed in this paper, and the implications of these results for fuel processing are described.
Date: August 22, 1999
Creator: Birtt, P.F. & Buchanan, A.C., III
Partner: UNT Libraries Government Documents Department

Radicals of a Ring

Description: The problem with which this investigation is concerned is that of determining the properties of three radicals defined on an arbitrary ring and determining when these radicals coincide. The three radicals discussed are the nil radical, the Jacobsson radical, and the Brown-McCoy radical.
Date: May 1971
Creator: Crawford, Phyllis Jean
Partner: UNT Libraries

Unimolecular reaction dynamics of free radicals

Description: Free radical reactions are of crucial importance in combustion and in atmospheric chemistry. Reliable theoretical models for predicting the rates and products of these reactions are required for modeling combustion and atmospheric chemistry systems. Unimolecular reactions frequently play a crucial role in determining final products. The dissociations of vinyl, CH2= CH, and methoxy, CH3O, have low barriers, about 13,000 cm-1 and 8,000 cm-1, respectively. Since barriers of this magnitude are typical of free radicals these molecules should serve as benchmarks for this important class of reactions. To achieve this goal, a detailed understanding of the vinyl and methoxy radicals is required. Results for dissociation dynamics of vinyl and selectively deuterated vinyl radical are reported. Significantly, H-atom scrambling is shown not to occur in this reaction. A large number of spectroscopic experiments for CH3O and CHD2O have been performed. Spectra recorded include laser induced fluorescence (LIF), laser excited dispersed fluorescence (LEDF), fluorescence dip infrared (FDIR) and stimulated emission pumping (SEP). Such results are critical for implementing dynamics experiments involving the dissociation of methoxy.
Date: September 1, 2006
Creator: Miller, Terry A.
Partner: UNT Libraries Government Documents Department

Free Radical Induced Oxidation, Reduction and Metallization of NiSi and Ni(Pt)Si Surfaces

Description: NiSi and Ni(Pt)Si, and of the effects of dissociated ammonia on oxide reduction was carried out under controlled ultrahigh vacuum (UHV) conditions. X-ray photoelectron spectroscopy (XPS) has been used to characterize the evolution of surface composition. Vicinal surfaces on NiSi and Ni(Pt)Si were formed in UHV by a combination of Ar+ sputtering and thermal annealing. Oxidation of these surfaces in the presence of either O+O2 or pure O2 at room temperature results in the initial formation of a SiO2 layer ~ 7 Å thick. Subsequent exposure to O2 yields no further oxidation. Continued exposure to O+O2, however, results in rapid silicon consumption and, at higher exposures, the kinetically-driven oxidation of the transition metal(s), with oxides >35&#506; thick formed on all samples, without passivation. The addition of Pt retards but does not eliminate oxide growth or Ni oxidation. At higher exposures, in Ni(Pt)Si surface the kinetically-limited oxidation of Pt results in Pt silicate formation. Substrate dopant type has almost no effect on oxidation rate. Reduction of the silicon oxide/metal silicate is carried out by reacting with dissociated NH3 at room temperature. The reduction from dissociated ammonia (NHx+H) on silicon oxide/ metal silicate layer shows selective reduction of the metal oxide/silicate layer, but does not react with SiO2 at ambient temperature.
Date: August 2010
Creator: Manandhar, Sudha
Partner: UNT Libraries

Theoretical studies of combustion dynamics. Final progress report, August 1, 1986--July 31, 1997

Description: The authors completed a number of projects during this period of time. This resulted in fifty nine publications, which are listed below. The major thrusts of this research are the development and application of quantum methods to the study of fundamental chemical processes of importance in gas-phase combustion. Broadly speaking the work falls into two categories. One is the development and application of reduced dimensionality theories of chemical reactions, and the other into studies of radical-radical reactions that proceed mainly via complex formation. The various projects in these two areas and their intersection are reviewed.
Date: March 1, 1998
Creator: Bowman, J.M.
Partner: UNT Libraries Government Documents Department