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FTIR Spectroscopic and Theoretical Study of the Photochemistry of Matrix-Isolated Coumarin.

Kus, Nihal; Breda, Susana; Reva, Igor; Tasal, Erol; Ogretir, Cemil; Fausto, Rui
Fonte: American Society for Photobiology Publicador: American Society for Photobiology
Tipo: Artigo de Revista Científica
ENG
Relevância na Pesquisa
27.03%
The infrared spectrum of monomeric unsubstituted coumarin (C9H6O2; 2 H-1-benzopyran-2-one), isolated in solid argon at 10 K is presented and assigned. The UV-induced ( λ > 200 nm) unimolecular photochemistry of the matrix-isolated compound was studied experimentally. Three main photoreactions were observed: (a) decarboxylation of the compound and formation of benzocyclobutadiene and CO2, with the Dewar form of coumarin as intermediate; (b) isomerization of the compound, leading to production of a conjugated ketene; and (c) decarbonylation, leading to formation of CO and benzofuran complex. Further decomposition of benzofuran to produce ethynol is suggested. Photochannels (a) and (b) correspond to those previously observed for matrix-isolated α-pyrone and its sulfur analogs ( Phys. Chem. Chem. Phys. 2004, 6, 929; J. Phys. Chem. A 2006, 110, 6415), while route (c) is similar to the UV-induced photochemistry of coumarin in the gaseous phase ( J. Phys. Chem. A 2000, 104, 1095). Interpretation of the experimental data is supported by extensive calculations performed at the B3LYP/6-311++G(d,p), MP2/6-31G(d,p) and MP2/6-311++G(d,p) levels. [ABSTRACT FROM AUTHOR].

UV-induced photochemistry of matrix-isolated 1-phenyl-4-allyl-tetrazolone

Frija, L. M. T.; Reva, I. D.; Gómez-Zavaglia, A.; Cristiano, M. L. S.; Fausto, R.
Fonte: The Royal Society of Chemistry Publicador: The Royal Society of Chemistry
Tipo: Artigo de Revista Científica
ENG
Relevância na Pesquisa
27.03%
The photochemistry and molecular structure of 1-phenyl-4-allyl-tetrazolone (PAT) was studied by FT-IR matrix isolation spectroscopy and DFT(B3LYP)/6-311++G(d,p) calculations. The spectrum of matrix-isolated PAT monomers agrees well with the sum spectrum of three conformers predicted theoretically. UV irradiation (λ > 235 nm) of matrix-isolated PAT induces three types of photofragmentation: (1) production of phenylazide and allyl-isocyanate, with phenylazide then losing N2 to yield 1-aza-1,2,4,6-cycloheptatetraene; (2) formation of phenyl-isocyanate and allylazide; (3) N2 elimination leading to formation of 1-allyl-2-phenyldiaziridin-3-one; this compound partially reacts further to form 1-allyl-1H-benzoimidazol-2(3H)-one. The observed photochemistry of the matrix-isolated PAT is distinct from the preferred photochemical fragmentation in solution, where 3,4-dihydro-3-phenylpyrimidin-2(1H)-one is produced as the primary photoproduct.

Tautomer Selective Photochemistry in 1-(Tetrazol-5-yl)ethanol

Ismael, A.; Cristiano, M. L. S.; Fausto, R.; Gómez-Zavaglia, A.
Fonte: American Chemical Society Publicador: American Chemical Society
Tipo: Artigo de Revista Científica
ENG
Relevância na Pesquisa
27.03%
A combined matrix isolation FTIR and theoretical DFT/B3LYP/6-311++G(d,p) study of the molecular structure and photochemistry of 1-(tetrazol-5-yl)ethanol [1-TE] was performed. The potential energy surface landscapes of the 1H and 2H tautomers of the compound were investigated and the theoretical results were used to help characterize the conformational mixture existing in equilibrium in the gas phase prior to deposition of the matrices, as well as the conformers trapped in the latter. In the gas phase, at room temperature, the compound exists as a mixture of 12 conformers (five of the 1H tautomer and seven of the 2H tautomer). Upon deposition of the compound in an argon matrix at 10 K, only three main forms survive, because the low barriers for conformational isomerization allow extensive conformational cooling during deposition. Deposition of the matrix at 30 K led to further simplification of the conformational mixture with only one conformer of each tautomer of 1-TE surviving. These conformers correspond to the most stable forms of each tautomer, which bear different types of intramolecular H-bonds: 1H-I has an NH···O hydrogen bond, whereas 2H-I has an OH···N hydrogen bond. Upon irradiating with UV light (λ > 200 nm), a matrix containing both 1H-I and 2H-I forms...

Theoretical chemistry: current applications to photochemistry and thermochemistry

Ornellas, Fernando R.
Fonte: SPRINGER; NEW YORK Publicador: SPRINGER; NEW YORK
Tipo: Artigo de Revista Científica
ENG
Relevância na Pesquisa
37.03%
A historical perspective is given contrasting challenges and advances in theoretical chemistry at the time the first issue of Theoretical Chemistry Accounts appeared in 1962 and the progress achieved since then as expressed in current state-of-the-art applications in photochemistry and thermochemistry.

Propriedades fotoquímicas e fotofísicas de novos materiais derivados quinolinas e di naftalimidas; Photochemistry and photophysical properties of new materials derivatives of quinolines and Di-naphtalimides

Guerta, Adelsimara Ceballos
Fonte: Biblioteca Digitais de Teses e Dissertações da USP Publicador: Biblioteca Digitais de Teses e Dissertações da USP
Tipo: Dissertação de Mestrado Formato: application/pdf
Publicado em 18/06/2007 PT
Relevância na Pesquisa
37.18%
Um dos temas modernos em fotoquímica em soluções aquosas é a observação de prototropismo de estados eletrônicos excitados. Resumidamente, moléculas orgânicas contendo grupamentos ácido-base quando excitadas, e cujo tempo de vida do estado excitado seja longo o suficiente, reações competitivas de transferência de prótons com as do processo de relaxação poderão ocorrer. No caso de aumento de acidez os compostos são denominados fotoácidos e no contrário fotobases. Este fenômeno é atribuído a um estado isoeletrônico da molécula no estado fundamental tendo sido descritos variações de até sete unidades de pKa. Do ponto de vista da investigação Físico-Química o estudo da circunvizinhança, na qual as espécies excitadas percorrem uma superfície de potencial seja na direção da reassociação seja na da ionização com posterior solvatação das mesmas, fornece uma importante ferramenta de análise de propriedades de micro ambiente. Esta possibilidade advém das excelentes propriedades espectrais dos grupos cromofóricos desta classe de compostos o que facilita o monitoramento das espécies transientes adicionado ao estágio técnico atual de medidas ultra-rápidas. Neste estudo enfocamos o estudo de derivados de quinolina (fotobase)...

Supramolecular photochemistry and solar cells

IHA,NEYDE YUKIE MURAKAMI
Fonte: Academia Brasileira de Ciências Publicador: Academia Brasileira de Ciências
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/03/2000 EN
Relevância na Pesquisa
37.47%
Supramolecular photochemistry as well as solar cells are fascinating topics of current interest in Inorganic Photochemistry and very active research fields which have attracted wide attention in last two decades. A brief outline of the investigations in these fields carried out in our Laboratory of Inorganic Photochemistry and Energy Conversion is given here with no attempt of an exhaustive coverage of the literature. The emphasis is placed on recent work and information on the above mentioned subjects. Three types of supramolecular systems have been the focus of this work: (i) cage-type coordination compounds; (ii) second-sphere coordination compounds, exemplified by ion-pair photochemistry of cobalt complexes and (iii) covalently-linked systems. In the latter, modulation of the photoluminescence and photochemistry of some rhenium complexes are discussed. Solar energy conversion and development of thin-layer photoelectrochemical solar cells based on sensitization of nanocrystalline semiconductor films by some ruthenium polypyridyl complexes are presented as an important application that resulted from specifically engineered artificial assemblies.

Flow photochemistry: Old light through new windows

Knowles, Jonathan P; Elliott, Luke D; Booker-Milburn, Kevin I
Fonte: Beilstein-Institut Publicador: Beilstein-Institut
Tipo: Artigo de Revista Científica
Publicado em 21/11/2012 EN
Relevância na Pesquisa
27.18%
Synthetic photochemistry carried out in classic batch reactors has, for over half a century, proved to be a powerful but under-utilised technique in general organic synthesis. Recent developments in flow photochemistry have the potential to allow this technique to be applied in a more mainstream setting. This review highlights the use of flow reactors in organic photochemistry, allowing a comparison of the various reactor types to be made.

Desenvolvimento de um reator fotoquímico aplicável no tratamento de efluentes fenólicos presentes na indústria do petróleo; Development of a photochemistry reactor applicable in the treatment of phenolic wastewaters present in the petroleum industry

Mota, André Luís Novais
Fonte: Universidade Federal do Rio Grande do Norte; BR; UFRN; Programa de Pós-Graduação em Engenharia Química; Pesquisa e Desenvolvimento de Tecnologias Regionais Publicador: Universidade Federal do Rio Grande do Norte; BR; UFRN; Programa de Pós-Graduação em Engenharia Química; Pesquisa e Desenvolvimento de Tecnologias Regionais
Tipo: Dissertação Formato: application/pdf
POR
Relevância na Pesquisa
37.03%
With water pollution increment at the last years, so many progresses in researches about treatment of contaminated waters have been developed. In wastewaters containing highly toxic organic compounds, which the biological treatment cannot be applied, the Advanced Oxidation Processes (AOP) is an alternative for degradation of nonbiodegradable and toxic organic substances, because theses processes are generation of hydroxyl radical based on, a highly reactivate substance, with ability to degradate practically all classes of organic compounds. In general, the AOP request use of special ultraviolet (UV) lamps into the reactors. These lamps present a high electric power demand, consisting one of the largest problems for the application of these processes in industrial scale. This work involves the development of a new photochemistry reactor composed of 12 low cost black light fluorescent lamps (SYLVANIA, black light, 40 W) as UV radiation source. The studied process was the photo-Fenton system, a combination of ferrous ions, hydrogen peroxide, and UV radiation, it has been employed for the degradation of a synthetic wastewater containing phenol as pollutant model, one of the main pollutants in the petroleum industry. Preliminary experiments were carrier on to estimate operational conditions of the reactor...

Estudo de técnicas para o tratamento alternativo de efluentes oleosos oriundos da industrialização da castanha de caju

Jerônimo, Carlos Enrique de Medeiros
Fonte: Universidade Federal do Rio Grande do Norte; BR; UFRN; Programa de Pós-Graduação em Engenharia Química; Pesquisa e Desenvolvimento de Tecnologias Regionais Publicador: Universidade Federal do Rio Grande do Norte; BR; UFRN; Programa de Pós-Graduação em Engenharia Química; Pesquisa e Desenvolvimento de Tecnologias Regionais
Tipo: Tese de Doutorado Formato: application/pdf
POR
Relevância na Pesquisa
27.18%
An evaluation project was conducted on the technique of treatment for effluent oil which is the deriving process to improve cashews. During the evaluation the following techniques were developed: advanced processes of humid oxidation, oxidative processes, processes of biological treatment and processes of adsorption. The assays had been carried through in kinetic models, with an evaluation of the quality of the process by means of determining the chemical demand of oxygen (defined as a technique of control by means of comparative study between the available techniques). The results demonstrated that the natural biodegradation of the effluent ones is limited, as result using the present natural flora in the effluent one revealed impracticable for an application in the industrial systems, independent of the evaluation environment (with or without the oxygen presence). The job of specific microorganisms for the oily composite degradation developed the viability technique of this route, the acceptable levels of inclusion in effluent system of treatment of the improvement of the cashew being highly good with reasonable levels of removal of CDO. However, the use combined with other techniques of daily pay-treatment for these effluent ones revealed to still be more efficient for the context of the treatment of effluent and discarding in receiving bodies in acceptable standards for resolution CONAMA 357/2005. While the significant generation of solid residues the process of adsorption with agroindustrial residues (in special the chitosan) is a technical viable alternative...

A THEORETICAL INVESTIGATION OF PROSPECTS FOR MODE SELECTIVE OVERTONE PHOTOCHEMISTRY (QUANTUM DYNAMICS)

HOLME, THOMAS ANTHONY
Fonte: Universidade Rice Publicador: Universidade Rice
ENG
Relevância na Pesquisa
27.18%
We present several related studies which probe the energy flow dynamics of overtone initiated photochemistry using theoretical methods. The nature of the classical dynamics for two model isomerization systems has been investigated with an assumed initially localized excitation to a high overtone vibration state of a bond oscillator. For these systems, the classical equations of motion are propagated and analyzed using nonlinear resonance theory. We find energy flows along resonance enhanced pathways leading to nonstatistical chemical reactivity. There exist, however, profound perturbations for both models due to nonresonant energy flow. It is concluded that this perturbation leads to significant complications which render mode selective photochemistry unobservable. Since most experimental investigations have been unable to identify nonstatistical behavior, these theoretical results are in agreement with the majority of previous observations. We identify therefore, the primary difficulty which prevents the observation of mode selectivity to be nonresonant energy flow. We also investigate the nature of the excitation dynamics of the overtone excitation process itself. Completely classical descriptions for this process are highly inaccurate...

The photochemistry of azocyclopropanes

Bodager, Gregory Allen
Fonte: Universidade Rice Publicador: Universidade Rice
ENG
Relevância na Pesquisa
27.18%
The photochemistry of a number of azocyclopropanes has been studied: cis-1-(methyl-trans-azo)-2-phenylcyclopropane, trans-10(methyl-trans-azo)-2-phenylcyclopropane, trans-azocyclopropane and cis-azocyclopropane. Direct irradiation into the lowest n $ ightarrowpi$* band led to nearly exclusive cis-trans isomerization of the azo group. Minor processes for the phenylcyclopropanes were cyclopropyl ring isomerization, rig expansion of 1-methyl-5-phenyl-2-pyrazoline and formation of styrene. These processes suggest formation of a biradical intermediate which is apparently not formed in the case of trans- and cis-azocyclopropane. Singlet sensitization of cis-1-(methyl-trans-azo)-2-phenylcyclopropane with benzene increased the quantum yields of the processes competing with azo group isomerization. The increased efficiencies indicate that the second excited state of the azoalkane contributed to the observed photochemistry. On the other hand, the second excited state of trans- and cis-azocyclopropane is not accessible to benzene singlet sensitization and so led to exclusive interconversion of the two azo isomers. Direct irradiation into the short wavelength UV band of trans- and cis-azocyclopropane in pentane produced more decomposition products than n $ ightarrowpi$* excitation. The efficiency of trans $ ightarrow$ cis azo group isomerization decreased at the expense of the C-N and cyclopropyl C-C homolyses. These two cleavages accounted for a large number of products including nitrogen...

Competing demands for a complex system : photosystem II repair, photoprotection and quantum yield

Veerman, John
Fonte: Brock University Publicador: Brock University
Relevância na Pesquisa
27.42%
Photosynthesis in general is a key biological process on Earth and Photo system II (PSII) is an important component of this process. PSII is the only enzyme capable of oxidizing water and is largely responsible for the primordial build-up and present maintenance of the oxygen in the atmosphere. This thesis endeavoured to understand the link between structure and function in PSII with special focus on primary photochemistry, repair/photodamage and spectral characteristics. The deletion of the PsbU subunit ofPSII in cyanobacteria caused a decoupling of the Phycobilisomes (PBS) from PSII, likely as a result of increased rates of PSII photodamage with the PBS decoupling acting as a measure to protect PSII from further damage. Isolated fractions of spinach thylakoid membranes were utilized to characterize the heterogeneity present in the various compartments of the thylakoid membrane. It was found that the pooled PSIILHCII pigment populations were connected in the grana stack and there was also a progressive decrease in the reaction rates of primary photochemistry and antennae size of PSII as the sample origin moved from grana to stroma. The results were consistent with PSII complexes becoming damaged in the grana and being sent to the stroma for repair. The dramatic quenching of variable fluorescence and overall fluorescent yield of PSII in desiccated lichens was also studied in order to investigate the mechanism by which the quenching operated. It was determined that the source of the quenching was a novel long wavelength emitting external quencher. Point mutations to amino acids acting as ligands to chromophores of interest in PSII were utilized in cyanobacteria to determine the role of specific chromophores in energy transfer and primary photochemistry. These results indicated that the Hl14 ligated chlorophyll acts as the 'trap' chlorophyll in CP47 at low temperature and that the Q130E mutation imparts considerable changes to PSII electron transfer kinetics...

VELOCITY MAP IMAGING APPARATUS FOR STUDIES ON THE PHOTOCHEMISTRY OF WATER ICE

WICKRAMASINGHE, PIYUMIE
Fonte: Quens University Publicador: Quens University
Tipo: Tese de Doutorado
EN; EN
Relevância na Pesquisa
37.29%
This work describes the design and development of a velocity map imaging apparatus that will be used to study the laser initiated photochemistry of water ice and other condensed phases. Experiments on methanol ice photolysis using a different apparatus at Kyoto University are described to give an appreciation of the photochemistry and the experimental parameters. Water deposited on a surface at temperatures below 140 K can form an amorphous solid. Amorphous solid water (ASW), which does not exhibit properties of a well-defined phase, is the most profuse phase of water found in astrophysical environments. Chemical characteristics of ASW - in particular its photochemistry - and the physical characteristics closely associated with the structure such as density and surface are reviewed. The correlations between the morphology and the growth conditions of ASW are also described. Methanol is also known to be a component on the icy mantle on interstellar grains. The effects of irradiating amorphous solid methanol by UV photons are discussed. Experiments at Kyoto University have been performed to detect state-selectively nascent OH and CH3 photofragments following photolysis at 157 nm. Information on the velocity distributions was obtained from time-of-flight measurements. At Queen’s University Velocity Map Imaging combined with resonance enhance multiphoton ionization (REMPI) will be used for quantum state-selective detection of the nascent photoproducts and their velocity distribution. To help automate the experiments “virtual instruments” have been created for the hardware components of the experiment using LabVIEW 8.6. The ion optics of the velocity map imaging spectrometer under construction at Queen’s have been characterized using the SIMION 7.0 software package...

Photochemistry in Terrestrial Exoplanet Atmospheres I: Photochemistry Model and Benchmark Cases

Hu, Renyu; Seager, Sara; Bains, William
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 25/10/2012
Relevância na Pesquisa
27.18%
We present a comprehensive photochemistry model for exploration of the chemical composition of terrestrial exoplanet atmospheres. The photochemistry model is designed from the ground up to have the capacity to treat all types of terrestrial planet atmospheres, ranging from oxidizing through reducing, which makes the code suitable for applications for the wide range of anticipated terrestrial exoplanet compositions. The one-dimensional chemical transport model treats up to 800 chemical reactions, photochemical processes, dry and wet deposition, surface emission and thermal escape of O, H, C, N and S bearing species, as well as formation and deposition of elemental sulfur and sulfuric acid aerosols. We validate the model by computing the atmospheric composition of current Earth and Mars and find agreement with observations of major trace gases in Earth's and Mars' atmospheres. We simulate several plausible atmospheric scenarios of terrestrial exoplanets, and choose three benchmark cases for atmospheres from reducing to oxidizing. The most interesting finding is that atomic hydrogen is always a more abundant reactive radical than the hydroxyl radical in anoxic atmospheres. Whether atomic hydrogen is the most important removal path for a molecule of interest also depends on the relevant reaction rates. We also find that volcanic carbon compounds (i.e....

Chemical Processes in Protoplanetary Disks II. On the importance of photochemistry and X-ray ionization

Walsh, Catherine; Nomura, Hideko; Millar, T. J.; Aikawa, Yuri
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 12/01/2012
Relevância na Pesquisa
27.29%
We investigate the impact of photochemistry and X-ray ionization on the molecular composition of, and ionization fraction in, a protoplanetary disk surrounding a typical T Tauri star. We use a sophisticated physical model, which includes a robust treatment of the radiative transfer of UV and X-ray radiation, and calculate the time-dependent chemical structure using a comprehensive chemical network. In previous work, we approximated the photochemistry and X-ray ionization, here, we recalculate the photoreaction rates using the explicit UV wavelength spectrum and wavelength-dependent reaction cross sections. We recalculate the X-ray ionization rate using our explicit elemental composition and X-ray energy spectrum. We find photochemistry has a larger influence on the molecular composition than X-ray ionization. Observable molecules sensitive to the photorates include OH, HCO+, N2H+, H2O, CO2 and CH3OH. The only molecule significantly affected by the X-ray ionization is N2H+ indicating it is safe to adopt existing approximations of the X-ray ionization rate in typical T Tauri star-disk systems. The recalculation of the photorates increases the abundances of neutral molecules in the outer disk, highlighting the importance of taking into account the shape of the UV spectrum in protoplanetary disks. A recalculation of the photoreaction rates also affects the gas-phase chemistry due to the adjustment of the H/H2 and C+/C ratios. The disk ionization fraction is not significantly affected by the methods adopted to calculate the photochemistry and X-ray ionization. We determine there is a probable 'dead zone' where accretion is suppressed...

An overview of snow photochemistry: evidence, mechanisms and impacts

Grannas, A. M.; Jones, A. E.; Dibb, J.; Ammann, M.; Anastasio, C.; Beine, H. J.; Bergin, M.; Bottenheim, J.; Boxe, C. S.; Carver, G.; Chen, G.; Crawford, J. H.; Dominé, F.; Frey, M. M.; Guzmán, M. I.; Heard, D. E.; Helmig, D.; Hoffmann, M. R.; Honrath,
Fonte: European Geosciences Union Publicador: European Geosciences Union
Tipo: Article; NonPeerReviewed Formato: application/pdf
Publicado em 29/03/2007
Relevância na Pesquisa
27.18%
It has been shown that sunlit snow and ice plays an important role in processing atmospheric species. Photochemical production of a variety of chemicals has recently been reported to occur in snow/ice and the release of these photochemically generated species may significantly impact the chemistry of the overlying atmosphere. Nitrogen oxide and oxidant precursor fluxes have been measured in a number of snow covered environments, where in some cases the emissions significantly impact the overlying boundary layer. For example, photochemical ozone production (such as that occurring in polluted mid-latitudes) of 3–4 ppbv/day has been observed at South Pole, due to high OH and NO levels present in a relatively shallow boundary layer. Field and laboratory experiments have determined that the origin of the observed NOx flux is the photochemistry of nitrate within the snowpack, however some details of the mechanism have not yet been elucidated. A variety of low molecular weight organic compounds have been shown to be emitted from sunlit snowpacks, the source of which has been proposed to be either direct or indirect photo-oxidation of natural organic materials present in the snow. Although myriad studies have observed active processing of species within irradiated snowpacks...

An overview of snow photochemistry: evidence, mechanisms and impacts

Grannas, A. M.; Jones, A. E.; Dibb, J.; Ammann, M.; Anastasio, C.; Beine, H. J.; Bergin, M.; Bottenheim, J.; Boxe, C. S.; Carver, G.; Chen, G.; Crawford, J. H.; Dominé, F.; Frey, M. M.; Guzmán, M. I.; Heard, D. E.; Helmig, D.; Hoffmann, M. R.; Honrath,
Fonte: European Geosciences Union Publicador: European Geosciences Union
Tipo: Article; PeerReviewed Formato: application/pdf
Publicado em 22/08/2007
Relevância na Pesquisa
27.18%
It has been shown that sunlit snow and ice plays an important role in processing atmospheric species. Photochemical production of a variety of chemicals has recently been reported to occur in snow/ice and the release of these photochemically generated species may significantly impact the chemistry of the overlying atmosphere. Nitrogen oxide and oxidant precursor fluxes have been measured in a number of snow covered environments, where in some cases the emissions significantly impact the overlying boundary layer. For example, photochemical ozone production (such as that occurring in polluted mid-latitudes) of 3–4 ppbv/day has been observed at South Pole, due to high OH and NO levels present in a relatively shallow boundary layer. Field and laboratory experiments have determined that the origin of the observed NOx flux is the photochemistry of nitrate within the snowpack, however some details of the mechanism have not yet been elucidated. A variety of low molecular weight organic compounds have been shown to be emitted from sunlit snowpacks, the source of which has been proposed to be either direct or indirect photo-oxidation of natural organic materials present in the snow. Although myriad studies have observed active processing of species within irradiated snowpacks...

Hydrocarbon photochemistry and Lyman alpha albedo of Jupiter

Yung, Yuk L.; Strobel, Darrell F.
Fonte: American Astronomical Society Publicador: American Astronomical Society
Tipo: Article; PeerReviewed Formato: application/pdf
Publicado em 01/07/1980
Relevância na Pesquisa
27.18%
A combined study of hydrocarbon and atomic hydrogen photochemistry is made to calculate self-consistently the Lɑ albedo of Jupiter. It is shown that the Lɑ emissions observed by Voyagers I and II can be explained by resonance scattering of sunlight. Precipitation-of energetic particles from the magnetosphere can provide the large required source of atomic hydrogen, although the contribution of direct particle excitation to the disk-averaged brightness is insignificant. The variability of the Lɑ brightness inferred from many observations in recent years is examined. The large difference in the brightness of the He 584 Å resonance line observed by Pioneer and Voyager is briefly discussed. Driving the photochemistry by solar ultraviolet radiation alone yields a maximum mixing ratio of C_2H_6 + C_2H_2 at 10^(-2) atm of about 4 x 10^(-6). The possibility of additional CH_4 dissociation from precipitation of magnetospheric particles is discussed. The photochemistry of C_2H_2 and C_2H_3 is sufficiently uncertain not to permit accurate calculations of their densities and the ratio C_2H_6/C_2H_2.

Photochemistry under Continuous Flow Conditions; Fotoquímica sob Condições de Fluxo Contínuo

Vagner D. Pinho; Universidade Federal do Rio de Janeiro; Leandro S. M. Miranda; Universidade Federal do Rio de Janeiro; Rodrigo Otavio M. A. de Souza; Universidade Federal do Rio de Janeiro
Fonte: Revista Virtual de Química Publicador: Revista Virtual de Química
Tipo: ; Formato: binary/octet-stream
Publicado em 07/01/2015 PT
Relevância na Pesquisa
37.18%
Flow photochemistry is a growing field and has shown many interesting applications in the recent years due to the versatility of the technique related to the flexibility on the construction of the apparatus needed for the required transformation. The use of available materials and commercial source of light makes it an attractive option to several organic chemists who want to start exploring the fruitful field of photochemical reactions. DOI: 10.5935/1984-6835.20150009; Fotoquímica em fluxo contínuo é um campo crescente e tem mostrado muitas aplicações interessantes nos últimos anos. A versatilidade da técnica está relacionada com a flexibilidade na construção dos aparatos necessários para a realização das transformações de interesse. O uso de materiais disponíveis em quaisquer laboratórios de síntese orgânica e o uso de fontes comerciais de luz faz com que esta seja uma opção atraente para qualquer químico orgânico que queira começar a explorar o campo das reações fotoquímicas. DOI: 10.5935/1984-6835.20150009

Photochemistry of Naphthoquinones; Fotoquímica de Naftoquinonas

Nanci C. de Lucas; Universidade Federal do Rio de Janeiro; Aurélio B. B. Ferreira; Universidade Federal Rural do Rio de Janeiro; José Carlos Netto-Ferreira; Instituto Nacional de Metrologia
Fonte: Revista Virtual de Química Publicador: Revista Virtual de Química
Tipo: ; Formato: binary/octet-stream
Publicado em 07/01/2015 PT
Relevância na Pesquisa
37.29%
Quinones are widely distributed in living organisms, are present in medicines and used as reagents by chemists. In nature, certain benzoquinones are so commonly found that they are called ubiquinones (ubiquitous); others, the plastoquinones, participate in the process of photosynthesis, without being directly excited by light. These processes will not be seen here. The participation of excited quinones in the generation of singlet oxygen and other reactive oxygen species (ROS) will be addressed. The photochemistry of quinones, which are colored compounds, has been studied since the mid- XIX century, with Klinger; in Part 1, after the Introduction, we will present a summary of the most relevant results, so far, mainly for naphthoquinones, starting with fundamental concepts of organic photochemistry of ketones. We will see, for example, how biological quinones can, when excited by light, deactivate without generating harmful reactive species. In Part 2 some of the spectroscopic techniques with lasers, used in contemporary photochemistry will be reviewed. And, finally, these techniques will be applied to the study of naphthoquinones related to natural products and the results will be discussed. DOI: 10.5935/1984-6835.20150020; As quinonas estão amplamente disseminadas nos organismos vivos...