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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

Rate coefficients and mechanistic analysis for the reaction of hydroxyl radicals with 1,1-dichloroethylene and trans-1,2-dichloroethylene over an extended temperature range

Description: Article on rate coefficients and mechanistic analysis for the reaction of hydroxyl radicals with 1,1-dichloroethylene and trans-1,2-dichloroethylene over an extended temperature range.
Date: July 17, 2001
Creator: Yamada, Takahiro; El-Sinawi, Abdulaziz; Siraj, Mohammad Masud, 1972-; Taylor, Philip H.; Peng, Jingping; Hu, Xiaohua et al.
Partner: UNT College of Arts and Sciences

The time evolution of a vortex-flame interaction observed via planar imaging of CH and OH

Description: Planar laser-induced fluorescence imaging diagnostics of OH and CH are used to examine a premixed laminar flame subjected to a strong line-vortex pair. Results are reported for a fuel-rcih lamiar CH{sub 4}-air-N{sub 2} rod-stabilized flame. The flow studied was highly reproducible, which enabled the use of phase-sampled imaging to provide time-resolved image sequences. Image sequences are shown for a condition sufficient to produce localized extinction of the primary flame. Results indicate that a breakage in the CH front is not preceded by any distinct change in the OH front. The structure of the CH and OH profiles during the transient leading up to, and through the breakage of the CH front do not appear to be consistent with the concept of a strained laminar flame.
Date: May 1, 1996
Creator: Nguyen, Quang-Viet & Paul, P.H.
Partner: UNT Libraries Government Documents Department

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

Shock tube study of the reactions of the hydroxyl radical with combustion species and pollutants. Final report

Description: Shock heating t-butyl hydroperoxide behind a reflected shock wave has proved to be as a convenient source of hydroxyl radicals at temperatures near 1000 K. We applied this technique to the measurement of reaction rate coefficients of OH with several species of interest in combustion chemistry, and developed a thermochemical kinetics/transition state theory (TK-TST) model for predicting the temperature dependence of OH rate coefficients.
Date: February 1, 1998
Creator: Cohen, N. & Koffend, J.B.
Partner: UNT Libraries Government Documents Department

Replacing chemicals in recycle mills with mechanical alternatives

Description: A high-intensity spark fired underwater decomposes a small amount of the water into hydroxyl radicals, which are strong oxidants. These are able to oxidize contaminants such as glue and wood pitch that enter paper recycling mills as a part of the incoming furnish and cost the industry several hundred million dollars. The sparking technique is safe, inexpensive, and is capable of treating large volumes of water, which makes it attractive for mill applications. Several mill trials were run. Sparking caused a decrease in the tack of the deposits in one case. Lower bleach use occurred in two other mills; sparking reduced the degree of ink reattachment to fiber. The payback for either application is attractive. Sparking induced deposition of contaminants in another mill, which is a positive development--if it can be controlled. The technique is also able to degas water and to oxidize odor-causing sulfur compounds. Although one unit has been purchased by a mill, second-order effects caused by the technology needs to be defined further before the technology can be broadly applied.
Date: July 1, 2002
Creator: Technology, Institute of Paper Science
Partner: UNT Libraries Government Documents Department


Description: The Henry's law type constants of OH and HO{sub 2} have not been experimentally determined for obvious reasons: it is extremely difficult to measure the concentrations of these reactive species in either the gas phase or the aqueous phase, let alone simultaneously in both phases. At a more fundamental level, because these radicals react rapidly in both phases, compared with mass-transfer rates characterizing typical laboratory multi-phase systems, the gas-liquid equilibrium which is necessary for such measurements to be feasible is typically not attainable. Consequently, the Henry's law constants of these radicals are traditionally evaluated from the free energy of solution, {Delta}{sub sol}G{sup 0}(X) accompanying the process of transferring a molecule X from the gas phase, denoted g, to the aqueous phase, a, i.e. X{sub g} {rightleftharpoons} X{sub a} (9.10); using the equation {Delta}{sub sol}G{sup o}(X) = -RT ln k{sub H} (9.11); {Delta}{sub sol}G{sup o}(X) is defined as {Delta}{sub sol}G{sup o}(X) = {Delta}{sub f}G{sup o}(X){sub a} - {Delta}{sub f}G{sup o}(X){sub g} (9.12) where the free energies of formation of X in the gas phase and in the aqueous phase are typically evaluated using thermochemical cycles.
Date: May 23, 2003
Creator: Lee, Y. N.
Partner: UNT Libraries Government Documents Department

Mechanisms for radiation damage in DNA. Progress report, June 1, 1994--May 31, 1995

Description: In this project we have proposed several mechanisms for radiation damage to DNA and its constituents, and have detailed a series of experiments utilizing electron spin resonance spectroscopy, HPLC, GC-mass spectroscopy and ab initio molecular orbital calculations to test the proposed mechanisms. The results from these various techniques have resulted in an understanding of consequences of radiation damage to DNA from the early ionization event to the production of non-radical lesions (discussed in detail in Comprehensive Report). In this year`s work we have found the hydroxyl radical in DNA`s hydration layer. This is an important result which impacts the hole transfer hypothesis and the understanding of the direct vs. indirect effect in DNA. Further we have found the first ESR evidence for sugar radicals as a result of direct radiation damage to DNA nucleotides in an aqueous environment. This is significant as it impacts the biological endpoint of radiation damage to DNA and suggests future work in DNA. Work with DNA-polypeptides show clear evidence for electron transfer to DNA from the polypeptide which we believe is a radioprotective mechanism. Our work with ab initio molecular orbital theory has gain insight into the initial events of radiation damage to DNA. Ab initio calculations have provided an understanding of the energetics involved in anion and cation formation, ion radical transfer in DNA as well as proton transfer with DNA base pair radical ions. This has been extended in this year`s work to new, more accurate values for the electron affinities of the DNA bases, understanding of the relative stability of all possible sugar radicals formed by hydrogen abstraction on the deoxyribose group, hydration effects on, thiol radioprotectors, and an ongoing study of radical intermediates formed from initial DNA ion radicals. During this fiscal year five articles have been published, three are in ...
Date: November 1, 1994
Creator: Sevilla, M.D.
Partner: UNT Libraries Government Documents Department

Atmospheric Radiation Measurement Program Facilities newsletter, March 2001.

Description: The February 1998 issue of this newsletter discussed the Measurement of Pollution in the Troposphere (MOPITT) instrument that was to be tested at the SGP CART site before being launched aboard a NASA satellite to make precise, detailed measurements of tropospheric carbon monoxide and methane from space. The instrument was successfully launched on NASA's Terra satellite on December 18, 1999, by an Atlas IIAS rocket from Vandenberg Air Force Base in California and began collecting data at the end of February 2000. The instrument was designed by Dr. Jim Drummond, a physicist at the University of Toronto. The MOPITT Validation Exercise (MOVE) Campaign is schedule to take place at the SGP site from April 30 to May 18, 2001. Researchers will measure carbon monoxide by using instruments onboard the DOE Cessna Citation aircraft and other instruments located at the SGP CART. The data gathered will be compared with those collected by the MOPITT instrument to validate its performance thus far. MOPITT, which is scheduled for a five-year mission, will provide the first long-term global measurements of carbon monoxide and methane gas levels in roughly the lowest 10 miles of the atmosphere. Carbon monoxide and methane and their roles as greenhouse gases in global warming are of great interest. Greenhouse gases can trap escaping heat from Earth's surface, potentially increasing atmospheric temperatures. Carbon monoxide is a by-product of combustion, resulting primarily from industrial processing or biomass burning. Carbon monoxide levels in the atmosphere have been rising, indicating a problem. Normally, carbon monoxide is removed from the atmosphere by the hydroxyl radical, which can react with and remove many pollutants from the air.
Date: March 23, 2001
Creator: Holdridge, D.J.
Partner: UNT Libraries Government Documents Department

Experimental determination of the HO-Br bond energy and its relevance to the stratospheric and tropospheric ozone cycles

Description: The HO-Br bond energy (and consequently the heat of formation of HOBr) has been determined experimentally for the first time. HOBr can be photolyzed in the stratosphere to form Br and OH, both of which can react with ozone, and destroy it. Previous calculations modeling stratospheric reactions have assumed a lower stability than that found in the current research. The stability of HOBr was determined by measuring the threshold for formation of Br{sup +} from this molecule, using photoionization mass spectrometry. Their work was supported by the Division of Chemical Sciences, Office of Basic Energy Sciences.
Date: February 1, 1996
Creator: Ruscic, B. & Berkowitz, J.
Partner: UNT Libraries Government Documents Department

Planar laser-induced fluorescence imaging of flame heat release rate

Description: Local heat release rate represents one of the most interesting experimental observables in the study of unsteady reacting flows. The direct measure of burning or heat release rate as a field variable is not possible. Numerous experimental investigations have relied on inferring this type of information as well as flame front topology from indirect measures which are presumed to be correlated. A recent study has brought into question many of the commonly used flame front marker and burning rate diagnostics. This same study found that the concentration of formyl radical offers the best possibility for measuring flame burning rate. However, primarily due to low concentrations, the fluorescence signal level from formyl is too weak to employ this diagnostic for single-pulse measurements of turbulent reacting flows. In this paper the authors describe and demonstrate a new fluorescence-based reaction front imaging diagnostic suitable for single-shot applications. The measurement is based on taking the pixel-by-pixel product of OH and CH{sub 2}O planar laser-induced fluorescence images to yield an image closely related to a reaction rate. The spectroscopic and collisional processes affecting the measured signals are discussed and the foundation of the diagnostic, as based on laminar and unsteady flame calculations, is presented. The authors report the results of applying this diagnostic to the study of a laminar premixed flame subject to an interaction with an isolated line-vortex pair.
Date: December 12, 1997
Creator: Paul, P.H. & Najm, H.N.
Partner: UNT Libraries Government Documents Department

Saturated polarization spectroscopy with a picosecond laser for quantitative concentration measurements

Description: The collisional dependence of saturated polarization spectroscopy with a picosecond laser is investigated by probing hydroxyl in a flow cell. While nanosecond lasers have been used often for nonlinear diagnostic measurements of flame composition, picosecond lasers provide a potentially superior source for such techniques. Compared to a nanosecond laser, picosecond lasers produce significantly greater peak power for the same pulse energy, and this could improve the signal strength of multi-photon techniques such as degenerate four-wave mixing (DFWM) and polarization spectroscopy (PS). It has been suggested that the signal produced by such lasers would be less dependent on the collisional environment because the behavior of the molecular system probed by short-pulse lasers is governed more by the spectral width of the laser and the Doppler effect. To investigate the collisional dependence of the polarization spectroscopy signal generated with a picosecond laser, the authors probe the A{sup 2}{Sigma}{sup +}-X{sup 2}{Pi} (0,0) band of OH in a flow cell. In this well-controlled environment, the authors monitor the change in signal strength as they vary the buffer gas pressure by a factor of 50. Hydroxyl (OH) is created by photolysis of hydrogen peroxide using a Nd:YAG laser.
Date: February 11, 2000
Creator: Reichardt, T. A.; Farrow, R. L.; Teodoro, F. D. & Lucht, R. P.
Partner: UNT Libraries Government Documents Department

Measurements of nonmethane hydrocarbons in Phoenix, Arizona

Description: Nonmethane hydrocarbons (NMHCs) are precursors to oxidant formation. They are oxidized by hydroxyl radical (OH), forming a complex mixture of peroxy radicals that oxidize NO to NO{sub 2} without consuming ozone (O{sub 3}) and thus allow O{sub 3} to increase in the atmospheric boundary layer. The reactivities of the NMHCs that compose biogenic and anthropogenic emissions vary greatly. For example, isoprene, which is emitted by deciduous vegetation, has an atmospheric lifetime with respect to oxidation by OH of about 20 min in polluted air ([OH] = 10{sup 7} radicals cm{sup {minus}3}). The atmospheric lifetimes of 2-methylpropene, 2-methylbutane, and the xylenes, which are found in vehicle emissions, are approximately 30 min, 7 hr, and 1.5 hr, respectively. The authors made measurements of the NMHCs at a surface site and aloft aboard the Battelle Gulfstream (G-1) aircraft, as part of an air quality study in the Phoenix area during May 1998. Diurnal variations in the NMHC distributions and their propene-equivalent concentrations are used to examine origins and reactivities of the air masses that were sampled at the surface site.
Date: October 12, 1999
Creator: Doskey, P. V.; Kotamarthi, V. R. & Rudolph, J.
Partner: UNT Libraries Government Documents Department

Effect of Hydroxyl Concentration on Chemical Sensitivity of Polyvinyl Alcohol/Carbon-Black Composite Chemiresistors

Description: The sensitivity and selectivity of polyvinyl alcohol (PVA) / carbon black composite films have been found to vary depending upon the hydroxylation percentage ("-OH") of the polymer. These chemiresistors made from PVA films whose polymer backbone is 88% hydroxylated (PVA88) have a high sensitivity to water, while chemiresistors made from PVA75 have a higher sensitivity to methanol. The minor differences in polymer composition result in films with different Hildebrand volubility parameters. The relative responses of several different PVA-based chemiresistors to solvents with different volubility parameters are presented. In addition, polyvinyl acetate (PVAC) films with PVA88 are used in an array to distinguish the responses to methanol-water mixtures.
Date: May 19, 1999
Creator: Hughes, Robert C.; Patel, Sanjay V. & Yelton, W. Graham
Partner: UNT Libraries Government Documents Department

Evaluation of a novel multi-pass absorption cell for shock tube kinetic studies.

Description: The feasibility of using of a novel multi-pass absorption technique in combination with a shock tube for sensitive monitoring of free radicals for high-temperature kinetic studies was evaluated. The method was applied to study several elementary reactions of hydroxyl (OH) and methyl (CH{sub 3}) radicals.
Date: July 9, 2002
Creator: Krasnoperov, L. N. & Michael, J. V.
Partner: UNT Libraries Government Documents Department

Advanced fuel chemistry for advanced engines.

Description: Autoignition chemistry is central to predictive modeling of many advanced engine designs that combine high efficiency and low inherent pollutant emissions. This chemistry, and especially its pressure dependence, is poorly known for fuels derived from heavy petroleum and for biofuels, both of which are becoming increasingly prominent in the nation's fuel stream. We have investigated the pressure dependence of key ignition reactions for a series of molecules representative of non-traditional and alternative fuels. These investigations combined experimental characterization of hydroxyl radical production in well-controlled photolytically initiated oxidation and a hybrid modeling strategy that linked detailed quantum chemistry and computational kinetics of critical reactions with rate-equation models of the global chemical system. Comprehensive mechanisms for autoignition generally ignore the pressure dependence of branching fractions in the important alkyl + O{sub 2} reaction systems; however we have demonstrated that pressure-dependent 'formally direct' pathways persist at in-cylinder pressures.
Date: September 1, 2009
Creator: Taatjes, Craig A.; Jusinski, Leonard E.; Zador, Judit; Fernandes, Ravi X. & Miller, James A.
Partner: UNT Libraries Government Documents Department

Indoor Secondary Pollutants from Household Product Emissions inthe Presence of Ozone: A Bench-Scale Chamber Study

Description: Ozone-driven chemistry is a major source of indoor secondary pollutants of health concern. This study investigates secondary air pollutants formed from reactions between constituents of household products and ozone. Gas-phase product emissions were introduced along with ozone at constant rates into a 198-L Teflon-lined reaction chamber. Gas-phase concentrations of reactive terpenoids and oxidation products were measured. Formaldehyde was a predominant oxidation byproduct for the three studied products, with yields under most conditions of 20-30% with respect to ozone consumed. Acetaldehyde, acetone, glycolaldehyde, formic acid and acetic acid were each also detected for two or three of the products. Immediately upon mixing of reactants, a scanning mobility particle sizer detected particle nucleation events that were followed by a significant degree of ultrafine particle growth. The production of secondary gaseous pollutants and particles depended primarily on the ozone level and was influenced by other parameters such as the air-exchange rate. Hydroxyl radical concentrations in the range 0.04-200 x 10{sup 5} molecules cm{sup -3} were measured. OH concentrations were observed to vary strongly with residual ozone level in the chamber, which was in the range 1-25 ppb, as is consistent with expectations from a simplified kinetic model. In a separate test, we exposed the dry residue of two products to ozone in the chamber and observed the formation of gas-phase and particle-phase secondary oxidation products.
Date: October 1, 2005
Creator: Destaillats, Hugo; Lunden, Melissa M.; Singer, Brett C.; Coleman,Beverly K.; Hodgson, Alfred T.; Weschler, Charles J. et al.
Partner: UNT Libraries Government Documents Department

Quantum resonance effects in exchange, photodissociation, and recombination reactions

Description: This is the final report of a three-year, Laboratory-Directed Research and Development (LDRD) project at the Los Alamos National Laboratory (LANL). This project studied quantum resonance effects on chemical reactions. The authors accurate reactive scattering calculations showed that quantum resonance phenomena dominate most chemical reactions and are essential to any real understanding of reactivity. It was found that, as long-lived metastable states of the colliding system, resonances can decay to reactants, products, or a mixture of both. Only the latter contribute to reaction. Conditions under which resonances can be neglected or treated statistically were studied. Important implications about the mechanism of recombination reactions were discovered, and some remarkable effects of geometric phases on the symmetries and energies of resonances were also discovered. Calculations were completed for the reaction H + O{sub 2} {yields} OH + O, which is the rate limiting step in the combustion of all hydrocarbons and the single most important reaction in all of combustion chemistry.
Date: April 1, 1996
Creator: Pack, R.; Kendrick, B.; Kress, J.; Walker, R.; Hayes, E.; Lagana, A. et al.
Partner: UNT Libraries Government Documents Department

OH radical imaging in a DI diesel engine and the structure of the early diffusion flame

Description: Laser-sheet imaging studies have considerably advanced our understanding of diesel combustion; however, the location and nature of the flame zones within the combusting fuel jet have been largely unstudied. To address this issue, planar laser-induced fluorescence (PLIF) imaging of the OH radical has been applied to the reacting fuel jet of a direct-injection diesel engine of the ``heavy-duty`` size class, modified for optical access. An Nd:YAG-based laser system was used to pump the overlapping Q{sub 1}9 and Q{sub 2}8 lines of the (1,0) band of the A{yields}X transition at 284.01 nm, while the fluorescent emission from both the (0,O) and (1, I) bands (308 to 320 nm) was imaged with an intensified video camera. This scheme allowed rejection of elastically scattered laser light, PAH fluorescence, and laser-induced incandescence. OH PLIF is shown to be an excellent diagnostic for diesel diffusion flames. The signal is strong, and it is confined to a narrow region about the flame front because the threebody recombination reactions that reduce high flame-front OH concentrations to equilibrium levels occur rapidly at diesel pressures. No signal was evident in the fuel-rich premixed flame regions where calculations and burner experiments indicate that OH concentrations will be below detectable limits. Temporal sequences of OH PLIF images are presented showing the onset and development of the early diffusion flame up to the time that soot obscures the images. These images show that the diffusion flame develops around the periphery of the-downstream portion of the reacting fuel jet about half way through the premixed burn spike. Although affected by turbulence, the diffusion flame remains at the jet periphery for the rest of the imaged sequence.
Date: March 1996
Creator: Dec, J. E. & Coy, E. B.
Partner: UNT Libraries Government Documents Department

Implications of Berthlot`s descriptive of associative reactions

Description: Berthelot`s equation, k{sub {infinity}}(T) = A{sub {infinity}} exp (-Dk{sub B}T), provides a good description of the high-pressure rate coefficient for associative reactions such as CH{sub 3} + CH{sub 3}, CH{sub 3} + OH, and CH{sub 3} + H. The parameter D may be used to characterize an effective temperature-dependent barrier, {Delta}E{sub eff} = Dk{sub B}{sup 2}T{sup 2}, which is due to the internal energy, i.e. rotational and vibrational energy, or the centrifugal barrier of the associating species. The parameter A{sub {infinity}} may be identified as the rate coefficient for association when the species approach one another with zero translational and internal energy. A microcanonical rate expression is given which may be used to directly compare experimental results with theoretical calculations. In addition, this approach suggests that the Arrhenius expression for the high-pressure rate coefficient for dissociation should contain both the change of enthalpy of the reaction and this effective barrier.
Date: October 4, 1996
Creator: Hessler, J.P.
Partner: UNT Libraries Government Documents Department