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Kinetic and Thermochemical Studies of the Recombination Reaction Na + O₂ + N₂ from 590 to 1515 K by a Modified High-Temperature Photochemistry Technique

Description: Article on kinetic and thermochemical studies of the recombination reaction sodium + oxygen + nitrogen from 590 to 1515 K by a modified high-temperature photochemistry technique.
Date: September 1, 1989
Creator: Marshall, Paul & Narayan, A. S.
Partner: UNT College of Arts and Sciences

Photophysics and Photochemistry of Copper(I) Phosphine and Collidine Complexes: An Experimental/Theoretical Investigation

Description: Copper(I) complexes have been studied through both experimental and computational means in the presented work. Overall, the work focuses on photophysical and photochemical properties of copper(I) complexes. Photophysical and photochemical properties are found to be dependent on the geometries of the copper(I) complexes. One of the geometric properties that are important for both photochemical and photophysical properties is coordination number. Coordination numbers have been observed to be dependent on both ligand size and recrystallization conditions. The complexes geometric structure, as well as the electronic effects of the coordination ligands, is shown both computationally as well as experimentally to affect the emission energies. Two-coordinate complexes are seen to have only weak emission at liquid nitrogen temperature (77 K), while at room temperature (298 K) the two-coordinate complexes are not observed to be luminescent. Three-coordinate complexes are observed to be luminescent at liquid nitrogen temperature as well as at room temperature. The three-coordinate complexes have a Y-shaped ground (S0) state that distorts towards a T-shape upon photoexcitation to the lowest lying phosphorescent state (T1). The geometric distortion is tunable by size of the coordinating ligand. Luminescence is controllable by limiting the amount of non-radiative emission. One manner by which non-radiative emission is controlled is the amount of geometric distortion that occurs as the complex undergoes photoexcitation. Bulky ligands allow for less distortion than smaller ligands, leading to higher emission energies (blue shifted energies) with higher quantum efficiency. Tuning emission and increasing quantum efficiencies can be used to create highly efficient, white emitting materials for use in white OLEDS.
Date: August 2011
Creator: Determan, John J.
Partner: UNT Libraries

INVESTIGATION OF THE PHOTOCHEMICAL METHOD FOR URANIUM ISOTOPE SEPARATION

Description: To find a process for successful photochemical separation of isotopes several conditions have to be fulfilled. First, the different isotopes have to show some differences in the spectrum. Secondly, and equally important, this difference must be capable of being exploited in a photochemical process. Parts A and B outline the physical and chemical conditions, and the extent to which one might expect to find them fulfilled. Part C deals with the applicability of the process.
Date: July 10, 1943
Creator: Urey, H.C.
Partner: UNT Libraries Government Documents Department

Quantum symmetry and photoreactivity of azabenzenes

Description: The fundamental processes associated with a photochemical reaction are described with reference to experimental properties of azabenzenes. Consideration of both excitation and relaxation processes led to presentation of the symmetry propagator, a unifying principle which maps system fluctuations (perturbations acting on an initial state) with dissipations (transitions to different states), thus directing the energy flow along competing reactive and nonreactive pathways. A coherent picture of relaxation processes including chemical reactions was constructed with the aid of spectroscopic data. Pyrazine (1,4 diazine) possesses vibronically active modes which provide an efficient mechanism for internal conversion to the first excited singlet state, where other promoting modes of the correct symmetry induce both intersystem crossing to the triplet manifold, isomerization through diaza-benzvalene, and chemical reactions through cycloreversion of dewar pyrazine to yield HCN plus an azete. At higher energies simple H atom loss and internal conversion become more predominant, leading to ring opening followed by elimination of methylene nitrile and ground state reaction products. Efficiency of chemical transformations as dissipation mechanisms versus competing fluorescence, phosphorescence and radiationless relaxation was mapped from near ultraviolet to far ultraviolet by photodissociation quantum yields into reaction channels characterized by molecular beam photofragment translational spectroscopy. A reaction path model for azabenzene photochemistry was presented and tested against experiment. Presence of undiscovered channels in other azabenzene systems was predicted and verified. The dominant process, HCN elimination, was resolved into three distinct channels. Both molecular and atomic hydrogen elimination was observed, the former with significant vibrational excitation. Small yields of isomerization products, acetylene and N2, were also observed.
Date: June 1995
Creator: Chesko, J. D. M.
Partner: UNT Libraries Government Documents Department

Photochemical Silene Syntheses

Description: We report the attempted syntheses of two photochemical dimethylsilene precursors, both of which are derived from polyphenyl silanorbornadiene skeletons. Possible synthetic schemes and our results are reported herein. Photolysis of 1,2-divinyl-1,1,2,2-tetramethyl-1,2-disilane at room temperature in a cyclohexane solution of 1,3-butadiene produces 1,1-dimethyl-2-(vinyldimethylsilylmethyl) silene which is trapped in high yields to afford the E- and Z-1,1-dimethyl-2-(vinyldimethylsilylmethyl)-3-vinyl-1-silacyclobutanes in 42 and 29% yields, respectively, along with minor amounts of 1,1-dimethyl-2-(vinyldimethylsilylmethyl)-1-silacyclohex-3-ene, 9%. Low Pressure Flow Pyrolysis at 450º C of either the E- or Z-isomer provides a relatively mild thermal source of the silene in the gas phase. Two products, 1,1,3,3-tetramethyldisilacyclohex-3-ene and 2,2,5,5-tetramethyl-2,5-disilabicyclo[2.2.1]hexane, are formed from an intramolecular rearrangement of the silene. Other reactions of the 3-vinylsilacyclobutanes include geometric isomerization, ring expansion to the silacyclohex-3-ene, and a homodienyl-1,5-hydrogen shift to 3,3,6,6-tetramethyl-3,6-disiladeca-1,4,8-triene. Synthetic schemes, successful and unsuccessful, for hydrido silene, acylpolysilene, and fluorine substituted silene precursors are discussed in the final chapter.
Date: August 1987
Creator: Bobbitt, Kevin L. (Kevin Lee)
Partner: UNT Libraries

Proceedings of the Eighth DOE Solar Photochemistry Research Conference Held at Interlaken Conference Center, Lake Geneva, Wisconsin, June 11-14, 1984

Description: These annual meetings bring together contractors of the Division of Chemical Sciences in its basic research program on solar photochemical energy conversion to exchange information and to give interested government officials an opportunity to assess the current status of the program. This year's meeting was joined by 12 Canadian scientists with similar interests in solar photochemistry. This volume contains the program of the meeting, a list of attendees, the abstracts of 29 formal presentations and 36 posters, and a record of questions and answers following each presentation.
Date: November 1984
Creator: Argonne National Laboratory
Partner: UNT Libraries Government Documents Department

THE PHOTOCHEMISTRY OF PYRIDINE N-OXIDE

Description: The authors wish to report their results on the photolysis of pyridine N-oxide in alcoholic solution. Both methanol and ethanol solutions of pyridine N-oxide were irradiated. The reaction mixture was analyzed by gas-liquid chromatography (GLC) using a 2.5% FFAP on Chrom G column and a Porapak Q column. In order to collect the products, the volume of the photolysis solution was reduced in vacuo and the resulting mixture was separated by preparative GLC.
Date: September 14, 1967
Creator: Alkaitis, Algis & Calvin, Melvin.
Partner: UNT Libraries Government Documents Department

Chemistry of Mercury Species and Their Control in Coal Combustion

Description: Silica aggregates produced in a tubular aerosol reactor were classified according to the electrical mobility equivalent radius by differential mobility analyzer. Then E the classified aerosol was further analyzed by in situ light scattering measurement and TEM micrograph analysis to evaluate the properties of agglomerates, such as the radius of gyration, fractal dimension, primary particle diameter and number of primary particles. Based on the properties measured by the experiments, the actual surface area of the silica sorbent particles can be calculated.
Date: February 28, 1998
Partner: UNT Libraries Government Documents Department