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The mechanism for OH radical initiated atmospheric photoxidation reaction of ethyl acetate was carried out by using the density functional theory method. Geometries have been optimized at the B3LYP level with a standard 6-31G(d,p) basis set. The single-point energy calculations have been performed at the MP2/6-31G(d), MP2/6-311++G(d,p), and CCSD(T)/6-31G(d) levels, respectively. All of the possible degradation channels involved in the oxidation of ethyl acetate by OH radicals have been presented and discussed. Among the five possible hydrogen abstraction pathways of the reaction of ethyl acetate with OH radicals, the hydrogen abstractions from the C1-H3 and C2-H5 bonds are the dominant reaction pathways due to the low potential barriers and strong exothermicity. The β-ester rearrangement of IM6 is energetically favorable but is not expected to be important. The α-ester rearrangement reaction and [O.sub.2] direct abstraction from IM17 are the more favorable pathways and are strongly competitive. In addition, the α-ester rearrangement reaction is confirmed to be a one-step process. Acetic acid, formic acetic anhydride, acetoxyacetaldehyde, and acetic anhydride are the main products for the reaction of ethyl acetate with OH radicals. Key words: ethyl acetate, OH radicals, reaction mechanism, quantum chemical calculation. Le mecanisme de photo-oxydation atmospherique de l'acetate d'ethyle initie par le radical OH a ete mis en reuvre a l'aide de la theorie de fonctionnelle de la densite. Les geometries ont ete optimisees au niveau B3LYP avec une base standard 6-31G(d,p). Les calculs d'energie ponctuelle ont ete respectivement effectues aux niveaux MP2\6-31G(d), MP2\6-311++G(d,p) et CCSD(T)\6-31G(d). Toutes les chaines de degradation possibles impliquees dans l'oxydation de l'acetate d'ethyle par les radicaux OH ont ete presentees et etudiees. Parmi les cinq voies possibles d'extraction d'hydrogene de la reaction entre l'acetate d'ethyle et les radicaux OH, celles qui se produisent a partir des liaisons C1-H3 et C2-H5 sont les voies reactionnelles majoritaires en raison des faibles barrieres de potentiel et de la forte exothermicite. Le rearrangement du β-ester d'IM6 est energetiquement favorable mais ne devrait pas etre important. La reaction de rearrangement de l'α-ester et l'extraction directe d'[O.sub.2] a partir d'IM17 sont les voies reactionnelles les plus favorables et sont fortement competitives. En outre, la reaction de rearrangement de l'α-ester est confirmee comme etant un processus a une etape. L'acide acetique, l'anhydride formique-acetique, l'acetoxyacetaldehyde et l'anhydride acetique sont les principaux produits de la reaction entre l'acetate d'ethyle et les radicaux OH. [Traduit par la Redaction] Mots-cles: acetate d'ethyle, radicaux OH, mecanisme reactionnel, calcul de chimie quantique., Introduction Ethyl acetate (C[H.sub.3]C(O)OC[H.sub.2]C[H.sub.3]) is predominantly used as a solvent in surface coatings, adhesives, and inks and is also used as a process solvent in organic synthesis and pharmaceutical manufacture. [...]

As a common pharmaceutical and personal care product, ibuprofen (IBP) is regarded as an important pollutant in aqueous environments. In this paper, the OH-initiated advanced oxidation processes (AOPs) degradation mechanism and its subsequent reaction mechanism with IBP were studied at the M06-2x/6-311++G(2d, p)//M06-2x/6-31+G(d,p) level. The frontier electron density and bond dissociation energy were analyzed. In addition, profiles of the potential energy surface were constructed, and all the possible pathways were discussed. H-atom abstraction is the most important mechanism. The dominant products were IBAP, 2-[4-(1-hydroxyisobutyl)phenyl]propionic acid, and 1-(4-isobutylphenyl)-1-ethanol, which is in good agreement with the experimental results. Key words: OH radical, ibuprofen, degradation mechanism, DFT, aqueous environments. Produit de soin personnel et pharmaceutique commun, l'ibuprofene (IBP) est considere comme un polluant important des environnements aqueux. Dans le present article, le mecanisme de degradation des procedes d'oxydation avancee (POA) inities par le radical hydroxyle (OH) et les mecanismes reactionnels subsequents impliquant l'IBP ont ete etudies au niveau M06-2x/6-311++G(2d, p)//M06-2x/6-31+G(d,p). La densite electronique frontiere et l'energie de dissociation de liaison et l'energie de dissociation de liaison ont ete analysees. En outre, les profils de la surface d'energie potentielle ont ete etablis et toutes les voies reactionnelles possibles etudiees. L'extraction de l'atome d'hydrogene demeure le mecanisme le plus important. Les produits majoritaires etaient l'IBAP (4-isobutylacetophenone), l'acide 2-[4-(1-hydroxyisobutyl)phenyl]propionique et le 1-(4-isobutylphenyl)1-ethanol et concordaient bien avec les resultats experimentaux. [Traduit par la Redaction] Mots-cles : radical hydroxyle (OH), ibuprofene, mecanisme de degradation, TFD (theorie de la fonctionnelle de la densite), environnements aqueux., Introduction Pharmaceutical and personal care products are widely recognized as emerging environmental contaminants, which provides a new challenge to sewage and drinking water treatment systems. (1-3) Most of these compounds [...]

The chlorine-initiated reaction mechanism of ethyl formate in the atmosphere was investigated using the density functional theory method. The geometry parameters and frequencies of all of the stationary points were calculated at the B3LYP/ 6-31G(d, p) level. The single-point energy calculations were carried out at different levels, including MP2/6-31G(d), MP2/6-311++G(d, p), and CCSD(T)/6-31G(d). A detailed oxidation mechanism is provided and discussed. Present results show that α-ester rearrangement reaction and the [O.sub.2] direct abstraction from IM6 (HC(O)OCH(O)C[H.sub.3]) are the more favorable pathway and are competitive. The 1,4-H shift isomerization of IM6 proved to be feasible under general atmospheric conditions. The decomposition of IM18 (C[H.sub.3]C[H.sub.2]OC(O)O) is favorable both thermodynamically and kinetically. Canonical variational transition theory with small-curvature tunneling correction was employed to predict the rate constants. The overall rate constant of ethyl formate at 298 K is 8.63 x [10.sup.-12] [cm.sup.3] [molecule.sup.-1] [s.sup.-1]. The Arrhenius equations of rate constants at the temperature range of 200-380 K were fitted. Key words: ethyl formate, chlorine atom, reaction mechanism, kinetic parameters. Resume: Le mecanisme de reaction du formiate d'ethyle initie par le chlore dans l'atmosphere a ete etudie a l'aide de la theorie de la fonctionnelle de la densite. Les parametres geometriques et les frequences de tous les points stationnaires au niveau B3LYP/6-31G(d, p) ont ete calcules. Les calculs d'energie en un point fixe ont ete effectues a differents niveaux, parmi lesquels MP2/6-31G(d), MP2/6-311++G(d,p) et CCSD(T)/6-31G(d). Un mecanisme d'oxydation est expose et etudie de maniere approfondie. Les resultats actuels montrent que la reaction de rearrangement de l'[alfa]-ester et l'abstraction directe d'[O.sub.2] du compose IM6 (HC(O)OCH(O)C[H.sub.3]) sont les voies les plus favorisees et sontcompetitives. Ilest demontre que l'isomerisation du compose IM6 par le chngement 1,4-H est realisable sous conditions atmospheriques normales. La decomposition d'IM18 (C[H.sub.3]C[H.sub.2]OC(O)O) est thermodynamiquement et cinetiquement favorisee. La theorie de l'etat de transition variationnel canonique associee a une correction de l'effet tunnel avec faible courbure a ete employee pour predire les constantes de vitesse de reaction. Le formiate d'ethyle presente une constante de vitesse globale de 8,63 x [10.sup.-12] [cm.sup.3] [molecule.sup.-1] [s.sup.-1] a 298 K. Les equations d'Arrhenius ont permis de determiner les differentes constantes de vitesse dans l'intervalle de temperature compris entre 200 et 380 K. [Traduit par la Redaction] Mots-cles: formiate d'ethyle, atome de chlore, mecanisme reactionnel, parametres cinetiques., Introduction Ethyl formate (EF) (HC(O)OC[H.sub.2]C[H.sub.3]) is an important saturated ester and can be produced by many fruits and vegetables. Moreover, it occurs naturally in a variety of products, including essential [...]

The density functional theory (DFT) has been applied to studies on the homogeneous gas-phase degradation of 2,3,7,8-tetrachlorinated dibenzo-p-dioxins (2,3,7,8-TeCDD) initiated by the N[O.sub.3] radical, which is an important atmospheric species at night. The geometrical parameters and vibrational frequencies of all the stationary points were calculated at the MPWB1K/6-31+G (d,p) level. Potential energies were calculated at the MPWB1K/6-311+G (3df,2p) level. Three sites on 2,3,7,8-TeCDD react with the N[O.sub.3] radical with different barriers and reaction heats. The addition of N[O.sub.3] to the carbon atom on the central C-O ring is the most appropriate pathway and with the lower barriers, and the central ring of polychlorinated dibenzo-p- dioxin is opened in the subsequent reactions. Some other pathways are stressed for the dechlorination mechanism. Canonical variational transition-state theory with small curvature tunneling contribution was used to calculate the rate constants of each elementary reaction over the temperature range of 200-400 K. The Arrhenius equations were fitted to show the relationship between rate constants and temperature. Key words: 2,3,7,8-TeCDD, ≥N[O.sub.3] radical, atmospheric reaction mechanism, rate constant. Resume : On a applique la theorie de la fonctionnelle de la densite a l'etude de degradations en phase gazeuse homogene de 2,3,7,8-tetrachlorodibenzo-p-dioxines (2,3,7,8-TecDD), initiees par le radical N[O.sub.3,] une espece atmospherique importante la nuit. Les parametres geometriques et les frequences vibrationnelles de tous les points stationnaires ont ete calcules au niveau MPWB1K/6-31+G(d,p) de la theorie. On a calcule les energies potentielles au niveau MPWB1K/6-311+G(3df,2p). Il y a trois sites sur les 2,3,7,8-TeCDD qui reagissent avec le radical N[O.sub.3] avec des barrieres et des chaleurs de reactions differentes. L'addition du N[O.sub.3] sur l'atome de carbone du cycle C-O central correspond aux voies reactionnelles les plus appropriees avec de faibles barrieres et un noyau central de la dibenzo-p-dioxine polychloree qui s'ouvre dans les reactions subsequentes. On propose aussi quelques autres voies reactionnelles pour le mecanisme de dechloruration. Pour calculer les constantes de vitesse de chaque reaction elementaire sur la plage de temperature allant de 200 a 400 K, on a fait appel a la theorie de l'etat de transition variationnelle canonique avec une contribution par effet tunnel recourbe. Les equations d'Arrhenius ont ete ajustees pour montrer la relation entre les constantes de vitesses et la temperature. [Traduit par la Redaction] Mots-cles: 2,3,7,8-TeCDD, radical N[O.sub.3,] mecanisme de reaction atmospherique, constante de vitesse., Introduction Persistent organic pollutants have become a hot topic for their toxicity and widespread distribution in the environment. 2,3,7,8-Tetrachlorinated dibenzo-p-dioxin (2,3,7,8-TeCDD, or TeCDD) is the most toxic dioxin congener, owing [...]

Density functional theory (DFT) was used to study the β-myrcene ozonolysis reaction. The reactants, intermediates, transition states, and products were optimized at the MPWB1K/6-31G(d,p) level. The single-point energies were performed at the MPWB1K/6-311+G(3df,2p) level. The profiles of the potential energy surfaces were constructed and the rate constants of the reaction steps were analyzed. The possible reaction mechanisms for the ozonolysis intermediates in real atmosphere are also discussed. Based on quantum chemistry information, the rate constants were calculated using Rice-Ramsperger-Kassel-Marcus (RRKM) theory and the canonical variational transition-state theory (CVT) with small curvature tunneling effect (SCT). Arrhenius equations of rate constants over the temperature range of 200-800 K are provided, and the lifetimes of the reaction species in the troposphere were estimated according to rate constants. Key words: myrcene ozonolysis, DFT, RRKM theory, CVT/SCT, rate constant. On a fait appel a la theorie de la fonctionnelle de la densite (TFD) pour etudier la reaction d'ozonolyse du myrcene. On a optimise les reactifs, les intermediaires, les etats de transition et les produits au niveau MPWB1K/6-31G(d,p) de la theorie. On a determine des energies ponctuelles au niveau MPWB1K/6-311+G(3df,2p) de la theorie. On a construit les profils d' energie potentielle et on a analyse des constantes de vitesse des diverses etapes reactionnelles. On discute aussi des mecanismes potentiels des intermediaires d'ozonolyse dans un atmosphere reel. Sur la base des informations obtenues par la chimie quantique, on a calcule les constantes de vitesse a l'aide de la theorie de Rice-Ramsperger- Kassel-Marcus (RRKM) et de la theorie d' un etat de transition variationnel et canonique (TVC) comportant un effet tunnel avec faible courbure(TFC). On a obtenu les equations d'Arrhenius des constantes de vitesse sur la plage de temperature allant de 200 a 800 K et on a evalue les temps de vie des especes reactionnelles dans la troposphere a l' aide de ces constantes de vitesse. Mots-cles : ozonolyse du myrcene, theorie de la fonctionnelle de la densite (TFD), theorie de RRKM, theorie d'un etat de transition variationnel et canonique (TVC) comportant un effet tunnel avec faible courbure (TFC), constante de vitesse. [Traduit par la Redaction], Introduction β-Myrcene (7-methyl-3-methylene-1,6-octadiene) is an important member of the monoterpene family. Myrcene is produced by the mevalonic acid pathway of plants and emitted into the atmosphere through diffusion. (1) Myrcene [...]

The organophosphorous compound tabun is highly neurotoxic because of its irreversible inhibition on acetylcholinesterase (AChE). It is wildly used as a warfare agent in the military. In this work, the aging and reactivation mechanism of tabun-inhibited AChE were studied by using the quantum mechanical / molecular mechanical (QM/MM) method. Geometry optimization of the stationary points were performed at the B3LYP/6-31G(d) level. Single-point energies were computed at the B3LYP/6-311++G(d,p) level. On the basis of the QM/MM results, a conclusion that the C-O bond scission is caused by water attack on the ethoxy group in the aging mechanism can be drawn. The reactivation process initialed by the antidotes C[H.sub.2]N[O.sup.-] or HLO-7 consists of three elemental steps, the nucleophilic attack on the P atom by the antidote, the dephosphorylation process, and the decomposition of the antidote-tabun complex. The highest energy barriers of the aging reaction, C[H.sub.2]N[O.sup.-]-induced reactivation, and HLO-7-induced reactivation are 19.9, 20.0, and 14.8 kcal/mol (1 cal = 4.184 J), respectively. The relative lower overall energy barrier of HLO-7-induced reactivation compared with that of the aging reaction indicates that HLO-7 is able to reactivate tabun-inhibited AChE. In addition, whether a newly designed antidote is able to reactivate tabun-inhibited AChE can be examined by the inequation X < 19.9 kcal/mol, where X means the highest energy barrier of the reactivation reaction of the newly designed antidote. Key words: tabun, aging mechanism, reactivation mechanism, QM/MM method. Le tabun, un compose organophosphore, est extremement neurotoxique en raison de son inhibition irreversible de l'acetylcholinesterase (AChE). Il a ete utilise comme arme chimique. Dans ce travail, faisant appel a la methode de mecanique quantique / mecanique moleculaire (MQ/MM), on a etudie le vieillissement et le mecanisme de reactivation de de l'AChE inhibee par le tabun. On a effectue l'optimisation de la geometrie des points stationnaires au niveau B3LYP/6- 31G(d) de la theorie. On a calcule les energies des points uniques au niveau B3LYP/6-3111++G(d,p) de la theorie. Sur la base des resultats de methode de MQ/MM, il est possible d'arriver a une conclusion a l'effet que, dans le mecanisme de vieillissement, la scission de la liaison C-O est causee par l'attaque d'une molecule d'eau sur le groupe ethoxy. Le processus de reactivation initie par les antidotes C[H.sub.2]N[O.sup.-] ou HLO-7 comporte trois etapes elementaires, l'attaque nucleophile sur l'atome de phosphore par l'antidote, le processus de dephosphorylation et la decomposition du complexe antidote-tabun. La barriere d' energie la plus elevee de la reaction de vieillissement, la reactivation induite par le C[H.sub.2]N[O.sup.-] et la reactivation induite par le HLO-7 sont respectivement de 19,9, 20,0 et 14,8 kcal/mol (1 cal = 4.184 J). Le niveau relativement plus bas de l'energie d' activation globale pour la reactivation induite par le HLO-7 comparee a celle de la reaction de vieillissement indique que le HLO-7 peut reactiver l'AChE inhibee par le tabun. De plus, la possibilite qu'un nouvel antidote puisse reactiver l'AChE inhibee par le tabun a ete examinee par l'inequation X < 19,9 kcal/mol dans laquelle X correspond a la barriere d'energie la plus elevee de la reaction de reactivation du nouvel antidote mis au point. Mots-cles : tabun, mecanisme de vieillissement, mecanisme de reactivation, methode MQ/MM. [Traduit par la Redaction], Introduction Organophosphorus (OP) compounds, such as paraoxon, methamidophos, VX, and tabun, have been used as insecticides in modern agriculture or as chemical warfare agents in the military. The broad distribution [...]

In the atmosphere, linalool ozonolysis will generate a series of oxidation products and then form particles through nucleation. In this study, the linalool ozonolysis mechanisms were studied and some of the main products detected from experiment are verified. The Rice-Ramsperger-Kassel-Marcus (RRKM) theory and the canonical variational transition state theory (CVT) with small curvature tunneling effect (SCT) are used to calculate rate constants over the temperature range of 200~800 K. The total rate constant for the reaction of ozone with linalool is 4.50 x [10.sup.-16] [cm.sup.3] [molecule.sup.-1] [s.sup.-1], and the addition of ozone to [([CH.sub.3]).sub.2]C=CH- is the main ozone addition position. Furthermore, the Arrhenius formulas are fitted and the lifetimes of reaction species in the troposphere are discussed for the first time. The total atmospheric lifetime of linalool relative to O3 is 2.30 h. The [O.sub.3]-initiated atmospheric lifetimes of P1, P3, and P6 are 2.64 months, 16.67 days, and 15.5 h, respectively. Key words: linalool, ozonolysis reaction, rate constants, atmospheric lifetime. Dans l'atmosphere, l'ozololyse du linalol conduit a la formation d'une serie de produits d'oxydation qui, par nucleation, provoqueront la formation de particules. Dans cette etude, on a etudie les mecanismes d'ozonolyse du linalol et on a verifie la nature de quelques-uns des produits principaux formes au cours de ces experiences. On a fait appel a la theorie de Rice-Rampsperger-Kassel-Marcus (RRKM) et la theorie de l'etat de transition a variation canonique (TVC) modifiee par un leger effet tunnel de courbure (ETC) pour calculer les constantes de vitesse dans la plage de temperatures allant de 200 a 800 K. La constante de vitesse de reaction totale de l'ozone avec le linalol est de 4,50 x [10.sup.-16] [cm.sup.3] [molecule.sup.-1] [s.sup.-1] et l'addition de l'ozone sur le linalol se fait principalement sur la portion [([CH.sub.3]).sub.2]C=CH-. De plus, pour la premiere fois, on a ajuste les formules d'Arrhenius et on discute des temps de vie des especes reactives dans la troposphere. Le temps de vie total du linalol dans l'atmosphere, relatif a celui du O3, est de 2,30 jours. Les temps de vie atmospheriques inities par le [O.sub.3] des produits P1, P3 et P6 sont respectivement de 2,64 mois, 16,67 jours et 15,5 h. Mots-cles : reaction d'ozonolyse du linalol, constantes de vitesse, temps de vie atmospherique. [Traduit par la Redaction], Introduction Linalool [(([CH.sub.3]).sub.2]C=CH[CH.sub.2][CH.sub.2]C([CH.sub.3])(OH)CH=[CH.sub.2]), a monoterpene compound with a floral scent, is released into the atmosphere from certain types of vegetation, (1-3) including tea, oranges, grapes, mangos, lemons, tomatos, basil, and [...]

Abstract: The hydrogen-transfer reaction of HCO + HN[O.sub.2] → HCHO + N[O.sub.2] has been studied using both the density function theory (DFT) and high-level ab initio method. Three complete reaction [...]

We assessed the total nitrogen (N) concentrations of 28 still surface water (lake and pond), and 42 flowing surface water (river), monitoring sites under 29 typical terrestrial ecosystems of the Chinese Ecosystem Research Network (CERN) using monitoring data collected between 2004 and 2009. The results showed that the median total N concentrations of still surface water were significantly higher in the agro- (1.5 mg·L−1) and oasis agro- ecosystems (1.8 mg·L−1) than in the forest ecosystems (1.0 mg·L−1). This was also the case for flowing surface water, with total N concentrations of 2.4 mg·L−1, 1.8 mg·L−1 and 0.5 mg·L−1 for the agro-, oasis agro- and forest ecosystems, respectively. In addition, more than 50% of the samples in agro- and oasis agro- ecosystems were seriously polluted (>1.0 mg·L−1) by N. Spatial analysis showed that the total N concentrations in northern and northwestern regions were higher than those in the southern region for both still and flowing surface waters under agro- and oasis agro- ecosystems, with more than 50% of samples exceeding 1.0 mg·L−1 (the Class III limit of the Chinese National Quality Standards for Surface Waters) in surface water in the northern region. Nitrogen pollution in agro- ecosystems is mainly due to fertilizer applications, while the combination of fertilizer and irrigation exacerbates nitrogen pollution in oasis agro- ecosystems. [ABSTRACT FROM AUTHOR]

The interannual variation of the Bowen ratio, through its effect on the warming extent of available energy to the ecosystem land surface air, heavily influences the ecosystem microclimate and affects the hydrological cycle at both regional and global scales. Although the precipitation amount in southeast China is not expected to change greatly as a result of climate change, the precipitation frequency may be altered in the future. We explored the interannual variation of the Bowen ratio and its affecting mechanisms based on eddy covariance measurements in a subtropical plantation in southeast China during 2003–2012. The results indicated that the annual mean Bowen ratio was 0.35±0.06, with a range of 0.29–0.45. The Bowen ratio during the dry season (July-October) positively correlated with the annual Bowen ratio (R2 = 0.85, p<0.001). The effective precipitation frequency during the dry season, through its positive effect on shallow soil water content, indirectly and negatively affected the annual Bowen ratio. Between 2003 and 2012, the annual Bowen ratio exhibited a marginally significant decreasing trend (p = 0.061), meanwhile the effective precipitation frequency and shallow soil water content during the dry season increased significantly (p<0.001). The annual Bowen ratio may decrease further if the effective precipitation frequency and shallow soil water content during the dry season follow similar trends in the future. The warming effect of available energy to the surface air of our studied plantation may decline with the decreasing annual Bowen ratio. [ABSTRACT FROM AUTHOR]