Photolysis Of H2O2 Research Articles

New Flavonoid Glycosides from Chrozophora senegalensis and Their Antioxidant Activity

Bioassay-directed fractionation of an antioxidant methanol extract of the leaves of Chrozophora senegalensis using DPPH assay led to the isolation of three new flavonoid glycosides, quercetin 3-O-(6″-caffeoyl)-β-D-glucopyranoside-3′-O-β-D-glucopyranoside (1), quercetin 3-methyl ether-7-O-α-L-rhamnopyranosyl-(1→6)-(2″-p-coumaroyl)-β-D-glucopyranoside (2), acacetin 7-O-(6″-p-coumaroyl)-β-D-glucopyranoside (3), along with five known flavonoids, one phenolic derivative, and three megastigmane glycosides. Their structures were established on the basis of detailed spectral analysis. All isolated compounds were tested for their antioxidant activity on DPPH stable radical, superoxide anion, metal chelating activity, and DNA cleavage induced by the photolysis of H2O2. Quercetin 3-O-(6″-caffeoyl)-β-D-glucopyranoside-3′-O-β-D-glucopyranoside (1), quercetin 3′-methyl ether-3-O-α-L-rhamnopyranoside (4), and 4″'-methyl ether amenthoflavone (9) exhibited the highest antioxidant capacity being also able to modulate hydroxyl radical formation more efficiently than other compounds acting as direct hydroxyl radical scavengers and chelating iron.

Theoretical and Experimental Studies of the Spin Trapping of Inorganic Radicals by 5,5-Dimethyl-1-PyrrolineN-Oxide (DMPO). 1. Carbon Dioxide Radical Anion

The carbon dioxide radical anion (CO2*-) is known to be generated in vivo through various chemical and biochemical pathways. Electron paramagnetic resonance (EPR) spin trapping with the commonly used spin trap, 5,5-dimethyl-1-pyrroline N-oxide (DMPO), has been employed in the detection of CO2*-. The thermodynamics of CO2*- addition to DMPO was predicted using density functional theory (DFT) at the B3LYP/6-31++G**//B3LYP/6-31G* and B3LYP/6-311+G* levels with the polarizable continuum model (PCM) to simulate the effect of the bulk dielectric effect of water on the calculated energetics. Three possible products of CO2*- addition to DMPO were predicted: (1) a carboxylate adduct, (2) pyrroline-alcohol and (3) DMPO-OH. Experimentally, UV photolysis of H2O2 in the presence of sodium formate (NaHCO2) and DMPO gave an EPR spectrum characteristic of a C-centered carboxylate adduct and is consistent with the theoretically derived hyperfine coupling constants (hfcc). The pKa of the carboxylate adduct was estimated computationally to be 6.4. The mode of CO2*- addition to DMPO is predicted to be governed predominantly by the spin (density) population on the radical, whereas electrostatic effects are not the dominant factor for the formation of the persistent adduct. The thermodynamic behavior of CO2*- in the aqueous phase is predicted to be similar to that of mercapto radical (*SH), indicating that formation of CO2*- in biological systems may have an important role in the initiation of oxidative damage in cells.

Oxidative and Photochemical Stability of Ionomers for Fuel‐Cell Membranes

AbstractTo predict hydroxyl‐radical‐initiated degradation of new proton‐conducting polymer membranes based on sulfonated polyetherketones (PEK) and polysulfones (PSU), three nonfluorinated aromatics are chosen as model compounds for EPR experiments, aiming at the identification of products of HO.‐radical reactions with these monomers. Photolysis of H2O2 was chosen as the source of HO. radicals. To distinguish HO.‐radical attack from direct photolysis of the monomers, experiments were carried out in the presence and absence of H2O2. A detailed investigation of the pH dependence was performed for 4,4′‐sulfonylbis[phenol] (SBP), bisphenol A (= 4,4′‐isopropylidenebis[phenol]; BPA), and [1,1′‐biphenyl]‐4,4′‐diol (BPD). At pH ≥ pKA of HO. and H2O2, reactions between the model compounds and O2.− or 1O2 are the most probable ways to the phenoxy and ‘semiquinone’ radicals observed in this pH range in our EPR spectra. A large number of new radicals give evidence of multiple hydroxylation of the aromatic rings. Investigations at low pH are particularly relevant for understanding degradation in polymer‐electrolyte fuel cells (PEFCs). However, the chemistry depends strongly on pH, a fact that is highly significant in view of possible pH inhomogeneities in fuel cells at high currents. It is shown that also direct photolysis of the monomers leads to ‘semiquinone’‐type radicals. For SBP and BPA, this involves cleavage of a CC bond.

Product distributions from the OH radical‐induced oxidation of n‐pentane and isopentane (2‐methylbutane) in air

AbstractHydroxyl radicals, generated by photolysis of H2O2, were reacted with n‐pentane and isopentane in air in the absence of nitrogen oxides. The observed product distributions were compared with similar data derived by computer simulations, based on the known reaction mechanisms, to determine relative probabilities for hydrogen abstraction at different sites of the parent compounds and to estimate branching ratios and relative rate coefficients for cross‐combination reactions between different peroxy radicals. For n‐pentane, the distribution of the pentanols indicates probabilities for hydrogen abstraction, in percent, of q1 = 9.1 ± 0.7, q2 = 56.1 ± 1.8, and q3 = 34.8 ± 1.3, which agree with predictions based on the algorithm proposed by Atkinson. Branching ratios needed to harmonize calculated and observed product distributions are somewhat larger than, although still within the error ranges of, the values found by us previously. Comparison between experimental and calculated data confirms the isomerization and decomposition constants recently established for the three pentoxyl radical isomers. The product distribution for isopentane, which is dominated by acetone, acetaldehyde, 2‐methyl‐butan‐2‐ol, and 2‐methyl‐butan‐2‐hydroperoxide, is in harmony with the predicted oxidation mechanism. Probabilities for hydrogen abstraction from isopentane were estimated to occur to 12% at the primary, 28% at the secondary, and 60% at the tertiary sites, again in agreement with predictions based on the algorithm of Atkinson. © 2006 Wiley Periodicals, Inc. Int J Chem Kinet 38: 677–688, 2006

Effect of Vibrational Excitation on the Collisional Removal of Free Radicals by Atoms: OH(v=1) + N

The collisional removal of vibrationally excited OH(upsilon=1) by N(4S) atoms is investigated. The OH radical was prepared by 193 nm photolysis of H2O2, and N(4S) atoms were generated by a microwave discharge in N2 diluted in argon. The concentrations of OH(upsilon=0 and 1) were monitored by laser-induced fluorescence as a function of the time after the photolysis laser pulse. The N(4S) concentration was determined from the OH(upsilon=0) decay rate, using the known rate constant for the OH(upsilon=0) + N(4S) --> H + NO reaction. From comparison of the OH(upsilon=0 and 1) decay rates, the ratio of the rate constant k(upsilon=1)(OH-N) for removal of OH(upsilon=1) in collisions with N(4S) and the corresponding OH(upsilon=0) rate constant, k(upsilon=0)(OH-N) was determined to be 1.61 +/- 0.42, yielding k(upsilon=1)(OH-N) = (7.6 +/- 2.1) x 10(-11) cm3 molecule(-1) s(-1), where the quoted uncertainty (95% confidence limits) includes the uncertainty in k(upsilon=0)(OH-N). Thus, the collisional removal of OH(upsilon=1) by N(4S) atoms is found to be faster than for OH(upsilon=0).

Laboratory Study of O(1S) Formation Process in the Photolysis of O3 and its Atmospheric Implications

A high-sensitive technique to detect O(1S) atoms using vacuum ultraviolet laser-induced fluorescence (VUV-LIF) spectroscopy has been applied to study the O(1S) production process from the UV photodissociation of O3, N2O, and H2O2. The quantum yields for O(1S) formation from O3 photolysis at 215 and 220 nm are determined to be (1.4 ± 0.4) × 10−4 and (5 ± 3) × 10−5, respectively. Based on thermochemical considerations, the O(1S) formation from O3 photolysis at 215 and 220 nm is attributed to a spin-forbidden process of O(1S)+O2(X3Σg −). Analysis of the Doppler profile of O(1S) produced from O3 photolysis at 193 nm also indicates that the O(1S) atoms are produced from the spin-forbidden process. In the photolysis of N2O and H2O2 at 193 nm, no discernible signal of O(1S) atoms has been detected. The upper limit values of the quantum yields for O(1S) production from N2O and H2O2 photolysis at 193 nm are estimated to be 8 × 10−5 and 3 × 10−5, respectively. Using the experimental results, the impact of the O(1S) formation from O3 photolysis on the atmospheric OH radical formation through the reaction of O(1S)+H2O has been estimated. The calculated results show that the contribution of the O(1S)+H2O reaction to the OH production rate is ∼2% of that of the O(1D)+H2O reaction at 30 km altitude in mid-latitude. Implications of the present laboratory experimental results for the terrestrial airglow of O(1S) at 557.7 nm have also been discussed.

Kinetics of the Radical−Radical Reaction, O(3PJ) + OH(X2ΠΩ) → O2 + H, at Temperatures down to 39 K

The kinetics of the reaction between O atoms and OH radicals, both in their electronic ground state, have been investigated at temperatures down to ca. 39 K. The experiments employed a CRESU (Cinétique deRéaction en Ecoulement Supersonique Uniforme) apparatus to attain low temperatures. Both reagents were created using pulsed laser photolysis at 157.6 nm of mixtures containing H2O and O2 diluted in N2 carrier gas. OH radicals were formed by both direct photolysis of H2O and the reaction between O(1D) atoms and H2O. O(3P) atoms were formed both as a direct product of O2 photolysis and by the rapid quenching of O(1D) atoms formed in that photolysis by N2 and O2. The rates of removal of OH radicals were observed by laser-induced fluorescence, and concentrations of O atoms were estimated from a knowledge of the absorption cross-section for O2 at 157.6 nm and of the measured fluence from the F2 laser at this wavelength. To obtain a best estimate of the rate constants for the O + OH reaction, we had to correct the raw experimental data for the following: (a) the decrease in the laser fluence along the jet due to the absorption by O2 in the gas mixture, (b) the increase in temperature, and consequent decrease in gas density, as a result of energy released in the photochemical and chemical processes that occurred, and (c) the formation of OH(v = 0) as a result of relaxation, particularly by O2, of OH radicals formed in levels v > 0. Once these corrections were made, the rate constant for reaction between OH and O(3P) atoms showed little variation in the temperature range of 142 to 39 K and had a value of (3.5 +/- 1.0) x 10(-11) cm3 molecule(-1) s(-1). It is recommended that this value is used in future chemical models of dense interstellar clouds.

Modelling the impact of noctilucent cloud formation on atomic oxygen and other minor constituents of the summer mesosphere

Abstract. The formation, evolution and eventual sublimation of noctilucent clouds (NLC) may have a significant effect on the odd oxygen and hydrogen chemistry of the high latitude summer mesosphere. Three mechanisms are considered here: the direct uptake of atomic oxygen on the surface of the ice particles; the redistribution of water vapour, which changes the photochemical source of odd hydrogen species; and the direct photolysis of the ice particles themselves to produce odd hydrogen species in the gas phase. A 1-D photochemical model is employed to investigate the potential importance of these mechanisms. This shows, using the recently measured uptake coefficients of O on ice, that the heterogeneous removal of O on the surface of the cloud particles is too slow by at least a factor of 5x103 to compete with gas-phase O chemistry. The second and third mechanisms involve the solar Lyman-α photolysis of H2O in the gas and solid phase, respectively. During twilight, Lyman-α radiation is severely attenuated and these mechanisms are insignificant. In contrast, when the upper mesosphere is fully illuminated there is a dramatic impact on the O profile, with depletion of O at the base of the cloud layer of close to an order of magnitude. A correspondingly large depletion in O3 is also predicted, while H, OH, HO2 and H2O2 are found to be enhanced by factors of 3-5. In fact, rocket-borne mass spectrometer measurements during summer have revealed local H2O2 enhancements in the region of the clouds. Rocket-borne measurements of atomic O and O3 profiles in the presence of mesospheric clouds in the daytime are highly desirable to test the predictions of this model and our understanding of the genesis of mesospheric clouds.

The reaction of anthracene with OH radicals: An experimental study of the kinetics between 58 and 470K

The first direct measurement of the reaction rate constant of a polycyclic aromatic hydrocarbon in the gas phase in the temperature range 58-470 K is reported. The reaction is OH+ anthracene and the experiment has been performed in a continuous flow Cinetique de Reaction en Ecoulement Supersonique Uniforme apparatus, which had to be modified for this purpose. Pulsed laser photolysis of H(2)O(2) has been used to generate OH radicals and laser-induced fluorescence to observe the kinetic decay of the radicals and hence determine the rate coefficients. The reaction is found to be fast, and the rate constant increases monotonically as the temperature is lowered. The rate coefficients match the expression k(cm(3) molecules(-1) s(-1))=1.12 x 10(-10)(T/300)(-0.46).

Infrared OH Prompt Emission as a Proxy of Water Production in Comets: Quantitative Analysis of the Multiplet Near 3046 cm−1in Comets C/1999 H1 (Lee) and C/2001 A2 (LINEAR)

We report quantitative measurements of OH vibrational prompt emission in comets C/1999 H1 (Lee) and C/2001 A2 (LINEAR) based on high-dispersion infrared spectra acquired at the Keck Observatory atop Mauna Kea, Hawaii. Effective g-factors for four OH lines near 3046 cm-1 (in the 1-0 band) were obtained from simultaneous detections of OH and H2O. The measured spatial distribution of this OH quadruplet traces that of H2O, as expected if the excited OH is produced directly by water photolysis. These results establish OH prompt emission as an alternative (and convenient) proxy for water in comets. Possible limitations to the approach are discussed. Extension to other OH multiplets in the L band will permit direct comparison with theoretical models for the rotational population distribution of the free OH radicals produced by H2O photolysis in cometary atmospheres.

Antioxidant activity of extracts from Calocedrus formosana leaf, bark, and heartwood

Calocedrus formosana Florin (Cupressaceae) is an endemic tree to Taiwan. To evaluate the antioxidant activity of the plant extracts from heartwood, bark, and leaf of C. formosana, assays for 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical and superoxide anion scavenging activities, as well as prevention of DNA strand cleavage were performed in this study. Similar IC50 values against the DPPH radical were found for the heartwood and bark extracts at approximately 23 µg/ml. Moreover, the heartwood extract exhibited the highest inhibitory activity against superoxide radicals among the test samples; a 2.3-fold lower value of IC50 for superoxide radical inhibition was found in the heartwood extract relative to that of (+)-catechin. Much less effect on inhibition of DPPH and superoxide radicals was found from the leaf extract of C. formosana. More than 70% of superoxide radicals were inhibited in the presence of 10 µg/ml heartwood extract, whereas only 15% inhibition was obtained from the leaf extract. The heartwood extract, at a dose of approximately 0.5 mg/ml, apparently completely prevented the ΦX174 supercoiled DNA cleavage induced by ultraviolet photolysis of H2O2, as judged by agarose gel electrophoresis. This report also suggests that the antioxidant activities of the plant extracts of C. formosana are in good correlation with their phenolic contents.

Low-Temperature Reactions of OH Radicals with Propene and Isoprene in Pulsed Laval Nozzle Expansions

The kinetics of the reactions of OH radicals with propene and isoprene in N2 have been studied in the temperature range of 58−300 K in a Laval nozzle expansion. Laser-induced fluorescence of the OH radical that is formed in the photolysis of H2O2 at 193 nm has been detected. The determined rate constants (2 × 10-11 to 2 × 10-10 cm3 molecule-1 s-1) for the OH radicals reacting with excess propene and isoprene (2-methyl-1,3-butadiene) have been found to increase when the temperature is decreased. The room temperature rate constants are in agreement with the literature data. Below 120 K, a saturation of the rate constant for the case of propene and a turnover to a formally positive temperature dependence for isoprene have been observed. The observed negative temperature dependence and the course of the temperature dependence at very low temperatures for both reactions are discussed within the framework of the loose transition-state theory and a simple two-transition-state model.

Gas phase oxidation of benzene: Kinetics, thermochemistry and mechanism of initial steps

A new investigation of the primary steps of the benzene oxidation, involving complementary experimental and theoretical approaches, is presented. The reactions of the OH-adduct (hydroxy-cyclohexadienyl radical c-C6H6-OH) were investigated using laser flash photolysis and producing OH radicals by H2O2 photolysis at 248 nm. It is confirmed that the adduct is in equilibrium with the corresponding peroxy radical RO2, near atmospheric conditions, the measured equilibrium constant being: Kc,2b = (2.62 ± 0.24) × 10−19 cm3 molecule−1 at 295 K, with the temperature dependent expression: ln(Kc,2b/cm3 molecule−1) = −63.29 + 6049/T, obtained by using the calculated entropy of reaction. The rate constant of the association reaction yielding RO2 is: k2b = (1.31 ± 0.12) × 10−15 cm3 molecule−1 s−1. Calculated data are in agreement with those values. In addition, data analysis shows that the reaction c-C6H6-OH + O2 involves an irreversible loss of radical species, yielding phenol and other oxidation products, with the global rate constant: kloss = (2.52 ± 0.40) × 10−16 cm3 molecule−1 s−1. Quoted errors are statistical (2σ), the possible total errors on the above values being estimated at around 40%. By comparison with the kloss value, the rate constant for phenol formation, calculated using a combination of DFT and ab initio CCSD(T) methods, corresponds to a phenol yield of about 55%, in reasonable agreement with experimental observations. Thermochemical and kinetic parameters have been calculated for the formation and for the reactions of the two RO2 stereoisomers, cis and trans. They show that the observed equilibrium must involve the trans isomer, which is more stable and is formed more rapidly than the cis isomer. Calculations show that the only possible reactions of peroxy radicals, under atmospheric conditions, is cyclisation yielding a bicyclic radical. However, cyclisation of the RO2(trans) is calculated to be too slow, compared to the rate of the irreversible radical loss, whereas it is very fast in the case of the cis isomer and can lead readily to oxidation products. On the basis of those results, a reaction mechanism is proposed for the first steps of benzene oxidation, consistent with all experimental and theoretical data, and which accounts for the principal oxidation products observed.

Low-Temperature Kinetics of Reactions of OH Radical with Ethene, Propene, and 1-Butene

The kinetics of the reactions of the OH radical with ethene (k1), propene (k2), and 1-butene (k3) are studied over a temperature range of T = 96−296 K. The low-temperature environment is provided by a pulsed Laval nozzle supersonic expansion of nitrogen with admixed radical precursor and reactant gases. The OH radicals are produced by pulsed photolysis of H2O2 at 248 nm. Laser-induced fluorescence of the OH radicals excited in the (1,0) band of the A2Σ+−X2Πi transition is used to monitor the OH decay kinetics to obtain the bimolecular rate coefficients. At T = 296 K, the rate constants k1, k2, and k3 are also measured as a function of total pressure. The room-temperature falloff parameters are used as the basis for extrapolation of the low-temperature kinetic data, obtained over a limited range of gas number density, to predict the high-pressure limits of all three rate coefficients at low temperatures. The temperature dependence of the measured high-pressure rate constants for T = 96−296 K can be expressed as follows: k1,∞ = (8.7 ± 0.7) × 10-12(T/300)(-0.85±0.11) cm3 molecule-1 s-1; k2,∞ = (2.95 ± 0.10) × 10-11(T/300)(-1.06±0.13) cm3 molecule-1 s-1; k3,∞ = (3.02 ± 0.15) × 10-11(T/300)(-1.44±0.10) cm3 molecule-1 s-1. All three high-pressure rate constants show a slight negative temperature dependence, which is generally in agreement with both low-temperature and high-temperature kinetic data available in the literature. Implications to the atmospheric chemistry of Saturn are discussed. Incorporating the new experimental data on k1 in photochemical models of Saturn's atmosphere may significantly increase the predicted rate of photochemical conversion of H2O into C−O containing molecules.

Effect of collisions on one-color polarization spectroscopy of OH A 2Σ+–X 2Π

The effect of collisions on the magnitude of polarization spectroscopy (PS) signals from the OH radical on the A 2Σ+–X 2Π (0,0) band has been studied. OH was produced by the 266-nm photolysis of H2O2 and detected by one-color degenerate PS, using ≈5-ns pulses from a Nd:YAG pumped dye laser. Spectra with both circular and linear pump polarizations are reported, together with signal dependence on OH number density and pump pulse fluence. The relative line intensities in the spectra and measured square dependence on OH number density are consistent with a description of PS as a variant of four-wave mixing spectroscopy. The pump pulse fluence dependence is fitted well by literature saturation curves. The collisional dependence of the PS signal was investigated by adding increasing pressures of He, Ar, or N2 collider gases for fixed overlapping pump and probe pulses. The principal finding is the very rapid loss of the PS signal with increasing collider pressure. The resulting phenomenological rate constants are in the range 5–9×10−9 cm3 s−1. We discuss these rate constants with reference to the literature rotational energy transfer and dephasing rate constants. We propose that the very large observed values may be explained by the effect of elastic velocity changing collisions.

OH in the coastal boundary layer of Crete during MINOS: Measurements and relationship with ozone photolysis

Abstract. Hydroxyl radical (OH) concentrations were measured in August 2001 at Finokalia Station on the northeastern coast of Crete during the Mediterranean Intensive Oxidant Study (MINOS). OH was measured based on selected ion chemical ionization mass spectrometry (SI/CIMS) with a time resolution of 30 sec and signal integration of 5 min. The corresponding accuracy, precision, and detection limit were 20% (1σ), 11% (1σ), and 2.4 x 105 molecules cm-3 (2σ), respectively. OH levels showed a strong diurnal variability with high maxima (approximately 2 x 107 molecules cm-3) occurring around 13:30 LT (10:30 UTC) and nighttime values below the detection limit. Daily 24-hour average concentrations varied between 3.6-6.7 x 106 cm-3. For the total measurement period (6-21 August) the mean and standard deviation were 4.5 ± 1.1 x 106 cm-3. The OH data set is analyzed based on a classification into three periods: I: Aug 6-8, II: Aug 9-11, III: Aug 13-18. For each of the three periods the measured OH concentrations are described by the empirical function [OH] = a J(O1D)b, with J(O1D) being the ozone photolysis frequency and a = 1.4 x 1010 s cm-3, 1.7 x 1010 s cm-3, 2.2 x 1010 s cm-3, and b = 0.68, respectively. Taking into account the estimated precision of the OH measurements this empirical function using three values for a and one value for b explains 99% of the observed variance of OH. A detailed sensitivity analysis using a CH4-CO box model was performed to interpret this relationship, in particular the meanings of the pre-exponential factor a and the exponent b. It was found that the value of b which represents the total logarithmic dependence of [OH] on J(O1D) includes the individual contributions from the photolysis of O3, NO2, HCHO, HONO, and H2O2 which could be determined using the box model. For the conditions prevailing during the MINOS campaign the exponent b was found to be dominated by the contributions from O3- and NO2-photolysis. For the individual functional dependences between [OH] and J(O1D), [OH] and J(NO2), and J(NO2) and J(O1D) the partial logarithmic derivatives were determined to be 0.5, 0.6, and 0.3, respectively. Overall, the box model yields a value of 0.70 for the exponent b in very good agreement with the corresponding value derived from the empirical analysis of the measurements. This empirical approach in which the chemical air mass characteristics influencing the OH radical balance and thereby, the self-cleansing efficiency of the atmosphere, are represented by only two parameters which are constant over quite substantial time periods may be used in future experiments to test and compare OH measurements made in different atmospheric environments.

Extreme ultraviolet photolysis of CO2 ‐ H2O mixed ices at 10 K

Experimental results on the spectral identification of IR absorption features and the production and depletion column densities produced through EUV photolysis of H2O + CO2 (4:1) mixed ices at 10 K are reported. A tunable intense synchrotron radiation light source was employed to provide the required high flux EUV photons. In this study the photon wavelengths used to irradiate the icy sample were selected to coincide with the prominent solar lines at 58.4 nm and 30.4 nm. A FTIR spectrometer was employed to obtain the in situ IR absorbance spectra produced through EUV photolysis of a given ice sample. Photon‐induced chemical reaction products were primarily H2CO3 and CO. While new molecular species were formed, the original reactants were depleted, as expected. We report the yields for producing H2CO3 and CO and the yields for depleting the parent CO2 molecule through EUV photolysis of the mixed ices. We have searched for possible intermediate products H2CO and HCO, but could not positively identify their existences in the spectra. The results presented in this work are particular relevant to our understanding of chemical evolution and synthesis in H2O‐rich icy satellites of the giant planets, comets, the interstellar medium, molecular clouds, and protostellar regions.

Solid-Phase Formation of Interstellar Vinyl Alcohol

Motivated by the recent discovery of gas-phase interstellar vinyl alcohol, CH2=CH(OH), we present laboratory experiments on this molecule's solid-phase formation. Through a combination of reaction chemistry, infrared spectroscopy, isotopic substitution, thermal annealings, and independent syntheses, we have identified vinyl alcohol in proton-irradiated H2O + C2H2 ices and have measured its column density at ~15 K. UV photolysis of H2O + C2H2 ices at ~15 K also produces vinyl alcohol. It is suggested that vinyl alcohol is formed in interstellar ices and then ejected into the gas phase, where it might undergo additional reactions.

Degradation of carbendazim by UV/H 2 O 2 investigated by kinetic modelling

The transformation of the fungicide carbendazim (methyl-2 benzimidazole carbamate) induced by hydroxyl radical generated by the UV photolysis of H2O2 has been studied in dilute aqueous solution. The efficient reaction of hydroxyl radicals with carbendazim led to the rapid degradation of carbendazim. The study of reaction kinetics yielded a second order rate constant of 2.2±0.3 109 M−1 s−1 for HO· radicals with carbendazim. This value is in agreement with a high reactivity of HO· radicals with carbendazim. Most degradation products were identified by high performance liquid chromatography mass spectrometry (HPLC-MS). In the presence of hydrogenocarbonate and carbonate ions, hydroxyl radicals were quenched and in turn carbonate radicals CO3·− were formed. Carbonate radicals are indeed known to react efficiently with compounds containing electron-rich sites such as nitrogen or sulfur atoms. The use of a kinetic modelling software gave evidence for the occurrence of such reactions with carbendazim. The second order rate constant of carbonate radical with carbendazim was equal to 6±2 106 M−1 s−1.

Decomposition of p-Chlorophenol in Aqueous Solution by Combination of Ultrasound and Ultraviolet Light

The decomposition performance of p-chlorophenol in aqueous solution by combination of ultrasound and ultraviolet light was examined. The decomposition of p-chlorophenol in aqueous solution was a pseudo-first-order reaction. The decomposition rate constant increased with increasing ultrasonic intensity and became lower as the initial concentration increased. The p-chlorophenol in aqueous solution was decomposed by OH radicals and photolysis. The synergy effect between ultrasound and ultraviolet light was observed. It was considered that the amount of OH radicals increased due to the photolysis of H2O2, which formed from the sonolysis of water. The decomposition of p-chlorophenol was simply modeled and kinetic analysis was performed. The calculated results were agreed with the experimental data.