field elastically scattered by the surrounding atoms; as the photoelectron energy, and thus the photoelectron wavelength, changes, individual scattering paths switch in and out of phase, so the observed modulations are directly related to the positions of the near-neighbor atoms relative to the emitter. In the present study, the intensity of the O 1s photoemission peak as a function of the photon energy was measured in nine inequivalent emission directions. These data have been analyzed to establish the local adsorption geometry of the 共 bonding 兲 oxygen atoms of the OH radicals on the Si(100)(2 ⫻ 1) surface, using a combination of a model-free direct-inversion method followed by more quantitative analysis using multiple-scattering cluster simulations to es- tablish the structural parameter values giving the best fit to the experimental PhD modulation curves.
The atmosphere, combustion, and interstellar space are some of the environments where the hydroxyl radical 共OH兲 plays an important role. Typically, laboratory and field mea- surements of OH radicals are achieved through laser-induced fluorescence 共LIF兲 detection on various well-characterized A 2 ⌺ + -X 2 ⌸ transitions. 1–5 The utility of the A-X band system is limited to the detection of low vibrational levels of the X 2 ⌸ state, namely, v ⬙ 艋 4, 6 due to Frank-Condon factors that favor diagonal transitions and electronic predissociation in the A 2 ⌺ + state. More recently, the B 2 ⌺ + -X 2 ⌸ system has been developed for LIF detection of higher vibrational levels of the X 2 ⌸ state 共6 艋 v ⬙ 艋 15兲. 7–11 Nevertheless, certain ap- plications, such as crossed molecular-beam scattering 12,13 and ultracold molecule studies, 14,15 would benefit from even more sensitive detection of OH radicals, such as might be provided by a resonance-enhanced ionization scheme.
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Howes, NUM, Lockhart, J, Blitz, M orcid.org/0000-0001-6710-4021 et al. (6 more authors) (2016) Observation of a New Channel, the Production of CH3, in the Abstraction Reaction of OH Radicals with Acetaldehyde. Physical Chemistry Chemical Physics, 18 (36). pp. 26423-26433. ISSN 1463-9076
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© 2018 Wiley Periodicals, Inc. This is the peer reviewed version of the following article: Bejan, IG, Winiberg, FAF, Mortimer, N et al. (5 more authors) (2018) Gas-phase rate coefficients for a series of alkyl cyclohexanes with OH radicals and Cl atoms. International Journal of Chemical Kinetics, 50 (8). pp. 544-555, which has been published in final form at https://doi.org/10.1002/kin.21179. This article may be used for non-commercial
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13 take the minor OH(v=1) and O( 1 D) contributions into account. A concentration dependent parameter was use to adjust the methyl yields. This analysis lowered the methyl radical yield for the chemically activated acetyl fragmentation by approximately 20 %, giving a new Y CH3 =
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Accordingly, the effect of fluorine substitution is more profound on values of activation enthalpies. The effect of fluorine-induced stabilisation has also been reported for decarboxylation of fluorinated carboxylic acids. 9 3.2. Ambient rate constants for FTOHs reactions with and their corresponding atmospheric half-life times: Based on findings of the previous section and the experimental observation of the predominance of abstraction via channels A and B, we calculate herein the ambient rate constants for the reactions of FTOHs with OH radical, by applying the conventional transition stet theory. Our calculations yield energetic paramaters obtained at the BB1IK/GTLarge/BB1K/6-311+G(d,p) level of theory. Effects of tunnelling and internal rotations are included in the derivation of the reaction rate constants. Reaction rate constants, energetic parameters and atmospheric half-lives (based on [OH] = 1.0 × 10 6 molecule cm -3 ) are given in Table 1. Generally, our calculated ambient rates are in a satisfactorily agreement with the corresponding experimental values for FTOHs; including CF 3 CF 2 CH 2 OH (1.05 × 10 -13 cm 3 molecule -1 s -1 ) and CF 3 CH 2 CH 2 OH (8.90 × 10 -13 cm 3
in the cross-sections at various collision energies at high rota- tional levels but sometimes the reverse is true at low rota- tional levels, and this is related to the rotational dependence of the degree of electron alignment (Macdonald & Liu 1989). Also, a propensity for spin-orbit manifold conserving transitions over spin-orbit manifold changing transitions was not observed in agreement with previous work on purely rotational excita- tion (Marinakis et al. 2015). Although a detailed discussion of propensities is beyond the scope of this work, a visual com- parison between rate coe ffi cients for spin-orbit conserving and spin-orbit changing (left and right), and e → e versus e → f transitions for He–CH / OH collisions is shown in Figs. 7 and 8, respectively. The initial level was chosen to be the lowest e level in the lowest spin-orbit manifold with the highest F quantum number, that is j = 0.5e, F = 1 for CH, and j = 1.5e, F = 2 for OH. Di ff erent choices of the initial level can be considered in order to examine all the propensities. The final levels were from j = 2.5 to 6.5. Some of these rates are shown in Figs. 7 and 8. From these He–CH collisions, on average, the propensity is for final levels in 2 Π
The rate of photo-Fenton degradation was found to increase with increase concentration of catalyst. Optimum value for the amount of different pillared clay samples was found to be 0.12 g. This can be explained on the basis that on increase amount of pillared clay sample results into increase in rate of eq. (ii). But after a certain limit, a reverse trend was observed. This may be explained on the basis that on increasing amount of clay sample results into increase in concentration of Fe 3+ ions, this results into increase in the rates of eq. (3) generating • OOH radical, which consumed more amount of Fe 3+ ions and hence, Fe 3+ ions are now less available for generation of • OH radicals and the rate of photodegradation also decreases.
Abstract. A new chemical mechanism for the oxidation of biogenic volatile organic compounds (BVOCs) is presented and implemented in the Model of Atmospheric composition at Global and Regional scales using Inversion Techniques for Trace gas Emissions (MAGRITTE v1.1). With a total of 105 organic species and over 265 gas-phase reactions, 69 pho- todissociations, and 7 heterogeneous reactions, the mecha- nism treats the chemical degradation of isoprene – its main focus – as well as acetaldehyde, acetone, methylbutenol, and the family of monoterpenes. Regarding isoprene, the mecha- nism incorporates a state-of-the-art representation of its oxi- dation scheme accounting for all major advances put forward in recent theoretical and laboratory studies. The recycling of OH radicals in isoprene oxidation through the isomer- ization of Z-δ-hydroxyperoxy radicals is found to enhance OH concentrations by up to 40 % over western Amazonia in the boundary layer and by 10 %–15 % over the south- eastern US and Siberia in July. The model and its chem- ical mechanism are evaluated against the suite of chem- ical measurements from the SEAC 4 RS (Studies of Emis- sions and Atmospheric Composition, Clouds and Climate Coupling by Regional Surveys) airborne campaign, demon- strating a good overall agreement for major isoprene oxida- tion products, although the aerosol hydrolysis of tertiary and non-tertiary nitrates remain poorly constrained. The com- parisons for methylnitrate indicate a very low nitrate yield (< 3 × 10 −4 ) in the CH 3 O 2 + NO reaction. The oxidation of
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Keeping all other factors identical, the concentration of catalyst was changed and its effect on the rate of photochemical degradation was observed. The result of Fig.5 reveals that the rate of photobleaching of dye increases with the increase in the concentration of Fe +3 ions up to 2.65 x 10 -4 M. The increase in Fe +3 ions in the reaction mixture are accompanied by enhanced generation of . OH radicals, consequently increasing the rate of photdegradation. After the optimal Fe +3 additions, the higher dose of Fe +3 resulted in a brown turbidity that causes the recombination of . OH radicals and Fe +3 reacts with . OH as a scavenger. Therefore, on further increase, the rate becomes almost constant.
Colored wastewater is one of the most important sources of environmental pollution and because of their visibility and bearing toxic chemicals, it is very important to be treated before released into the environment. In recent years, several methods have been used for treatment of dyestuff effluents. In this work, removal of two azo dyes, Acid Orange 7 and Reactive Black 5 as an indicator of synthetic dyes by Fenton-like reaction were studied. In this process, OH radicals will be generated by using 0
intermediates were further identified by MS. The results presented in the Table 1 indicate that the ion of the molecule MO (1) is attacked by the free hydroxyl radicals formed by the photoelectrocatalytic system (equations 1-4), to generate the species (4), (5), (6) and (8), where the MO molecule is directly oxidized; these new compounds continue be attacked by more free hydroxyl radicals, generating the oxidized species (3), (2) and (7) once the molecule has been oxidized, the free hydroxyl radicals again attack the molecule causing the rupture of the azo-type bond, and therefore, the fragmentation of the molecule in two parts generating the species (9), (10) and (11), afterwards these are still oxidized, causing the aromatic ring to break and generate the species (12), which subsequently breaks into molecules of very low m/z value that could not be detected 34.
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spectrophotometrically at 595nm 35 . TRAP Method: This method is defined as total radical trapping antioxidant parameter. The fluorescence of R- Phycoerythrin is quenched by ABAP (2, 2’-azo–bis (2 -amidino- propane) hydrochloride) as a radical generator. This quenching reaction is measured in presence of antioxidants. The antioxidative potential is evaluated by measuring the delay in decoloration 36 . Cytochrome C test: Superoxide anions were assayed spectrophotometrically by a cytochrome reduction method described by McCord and Fridovich (1969). Xanthine oxidase converts xanthine to uric acid and yields superoxide anions and these radicals directly reduce ferri- cytochrome C to ferro- cytochrome C, having an absorbance change at 550 nm. When test compounds showed superoxide scavenger activity, there was a decrease in the reduction of ferri-cytochrome C
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Endosperm weakening followed by seed germination requires cell wall weakening. This process involves cleavage of cell wall polymers or loosening of bonds between the polymers. Several molecular mechanisms have been proposed for endosperm weakening. Digestion of cell wall polysaccharides by hydrolytic enzymes is one mechanism. The main focus so far has been on β-1,4-mannanase (Bewley, 1997) and β-1,3- glucanase (Leubner-Metzger, 2003). Reactive Oxygen Species (ROS) produced in the cell wall play a role in endosperm weakening, which takes place before endosperm rupture. Peroxidase activity increases in the micropylar endosperm of tomato seeds prior to endosperm rupture (i.e. during endosperm weakening) (Morohashi, 2002).The cleavage of cell wall polymers by •OH not only takes place in the endosperm, but also plays a role in radicle elongation. The cell walls have to be loosened in order to allow cell elongation, caused by water uptake, which takes place when the water potential in the embryo is lower than that of the surrounding medium (Muller et al., 2007).
Oxidative Damage To DNA: ROS can cause oxidative damages to DNA of both nuclear and mitochondrial. The nature of damages include mainly base modification, deoxyribose oxidation, strand breakage, and DNA protein cross-links. Among the various ROS, hydroxyl radical generates various products from the DNA bases which mainly includes C-8 hydroxylation of guanine to form 8-oxo- 7,8 dehydro-2¢ deoxyguanosine and 2,6-diamino-4-hydroxy- 5- form amimodipyrimidine, 8-OH-adenine, 2-OH-adenine, thymine glycol, cytosine glycol etc. 12 For example, mutation
Since, electrochemical reactions can leads to the production of insulating films over the electrode surface, thus requiring greater over potentials, the effect of initial burden, on the removal efficiency must be evaluated. In this study, the hormone concentrations ranged from 2.62 to 3.21 mg/L, being observed that at higher initial burden the effective removal decreases for a fixed applied potential (Figure 4A). This result is consistent with insulating reactions over the electrode surface that are higher at higher concentrations. Such, polymeric reactions are higher at acidic than neutral or alkaline pH . Moreover, at neutral pH, the water electrolysis to generate hydroxyl radicals is favored, since they have equivalent amounts of H + and OH - ions in the reaction medium, as shown in equation:
Scavenging of hydroxyl radical is an important antioxidant activity because of very high reactivity of the OH radical, enabling it to react with a wide range of molecules found in living cells such as sugars, amino acids, lipids and nucleotides 23 . Thus, removing OH is very important for the protection of living systems. Fig. 4 shows that the hydroxyl radical scavenging activity of different concentrations of phloroglucinol . The IC 50 value of hydroxyl
overload of the CPM when OH concentrations in the reaction cell were high (t < 500 s). For some experiments where the initiation laser fluence was high (~ 10 17 photons cm -2 pulse -1 ), this overload was especially apparent. It is unclear if this overload was simply a result of the high OH concentration, or if it was related to an overload recovery problem of the CPM. If the former explanation were true, it would be possible to account for this overload by subtraction of the 2-laser OH signal from the 3-laser OH signal. However, the effects of the CPM overload were not reproducible, which tends to suggest that there were overload
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electrochemical system was applied to evaluate the treatment efficiency of Orange II degradation because the organic pollution caused by Orange II is of seriously environmental concern due to its high toxicity [2-3]. Furthermore, Orange II is a typical kind of azo-dye that is difficult to degraded by normal chemical and biological methods . In this research Orange II was chosen as a representative model to investigate because it is one of the most difficult-to-remove pollutants in wastewater treatment industry. On the other hand, some mechanism about the generation of active radicals in the presence of zeolite-TiO 2 on UV illumination are worth discussing in this study.
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Aerosols affect the earth's climate by absorbing or reflecting the Sun's energy (direct affect) and influencing cloud formation (indirect effect). They also degrade the local air quality thereby leading to potential health effects especially lung diseases such as asthma and cancer. Aerosols may be organic or inorganic, but most aerosol or much of the mass is organic in nature, particularly the PM 2.5 fraction. The influence of organic compounds on atmospheric aerosols is far less understood and largely uncertain, predominantly in relation to that of the dominant inorganic aerosol components . This is definitely caused by the large number (up to several hundred or a thousand) and structural complexity of the organic species involved, which are difficult to identify because of the difficulties associated with their collection, separation and the availability of suitable analytical methods. Primary organic aerosols, or POA, are directly emitted into the atmosphere through vehicle exhaust, cooking and biomass burning, whereas Secondary Organic Aerosols, or SOA, are formed from gas-to-particle conversion by oxidation of volatile organic compounds (VOC) present in the atmosphere. Oxidation mainly takes place with OH radicals, ozone or NO X . SOA
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