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Due to concerns surrounding its ozone depletion potential, there is a need for technologies to capture and destroy methyl bromide (CH3Br) emissions from postharvest fumigations applied to control agricultural pests. Previously, we described a system in which CH3Br fumes vented from fumigation chambers could be captured by granular activated carbon (GAC). The GAC was converted to a cathode by submergence in a high ionic strength solution and connection to the electrical grid, resulting in reductive debromination of the sorbed CH3Br. The GAC bed was drained and dried for reuse to capture and destroy CH3Br fumes from the next fumigation. However, the loose GAC particles and slow kinetics of this primitive electrode necessitated improvements. Here, we report the development of a cathode containing a thin layer of small GAC particles coating carbon cloth as a current distributor. Combining the high sorption potential of GAC for CH3Br with the conductivity of the carbon cloth current distributor, the cathode significantly lowered the total cell resistance and achieved 96% reductive debromination of CH3Br sorbed at 30% by weight to the GAC within 15 h at -1 V applied potential vs standard hydrogen electrode, a time scale and efficiency suitable for postharvest fumigations. The cathode exhibited stable performance over 50 CH3Br capture and destruction cycles. Initial cost estimates indicate that this technique could treat CH3Br fumes at -$5/kg, roughly one-third of the cost of current alternatives. [ABSTRACT FROM AUTHOR]

Bromomethane(CH3Br) is an acutely toxic environmentalpollutant that contributes to ozone depletion. Molecular simulationcould be a valuable tool for studying its partitioning and transportin the environment if an accurate molecular model was available. Thegeneralized Amber force field (GAFF), OPLS (optimized potentials forliquid simulations) force field, and CHARMM general force field (CGenFF)were tested for their ability to model the physical properties ofliquid bromomethane. The OPLS force field was in fairly good agreementwith experiment, while CGenFF and GAFF were significantly in error.The Br Lennard-Jones parameters of the GAFF and CGenFF models werereparameterized, but their radial distribution functions still havesignificant deviations from those calculated by ab initio moleculardynamics (AIMD). A Drude polarizable force field for bromomethanewas parametrized with an off-center positively charged site to representthe C–Br σ-hole. This model is in good agreement withthe bulk physical properties and the AIMD RDFs. The modest solubilityof bromomethane was reproduced by this model, with dispersion interactionsbeing the dominant water–solute interaction. The water–soluteelectrostatic interactions are a smaller factor in solubility. Thismodel predicts bromomethane to have a 13 kJ mol–1surface excess potential at the water–vapor interface. [ABSTRACT FROM AUTHOR]

Methyl bromide (CH3Br) is widely used as a fumigant for postharvest and quarantine applications for agricultural products at port facilities due to the short treatment period required, but it is vented from fumigation chambers to the atmosphere after its use. Due to the potential contributions of CH3Br to stratospheric ozone depletion, technologies for the capture and degradation of the CH3Br are needed to enable its continued use. Although granular activated carbon (GAC) has been used for CH3Br capture and thiosulfate has been used for destruction of CH3Br in aqueous solution, this research explored techniques for direct destruction of CH3Br sorbed to GAC. Submerging the GAC in an aqueous thiosulfate solution achieved debromination of CH3Br while sorbed to the GAC, but it required molar concentrations of thiosulfate because of the high CH3Br loading and produced substantial concentrations of methyl thiosulfate. Submergence of the GAC in water and use of the GAC as the cathode of an electrolysis unit also debrominated sorbed CH3Br. The reaction appeared to involve a one-electron transfer, producing methyl radicals that incorporated into the GAC. Destruction rates increased with decreasing applied voltage down to ~-1.2 V vs the standard hydrogen electrode. Cycling experiments conducted at -0.77 V indicated that >80% debromination of CH3Br was achieved over ~30 h with ~100% Coulombic efficiency. Sorptive capacity and degradation efficiency were maintained over at least 3 cycles. Capture of CH3Br fumes from fumigation chambers onto GAC, and electrolytic destruction of the sorbed CH3Br could mitigate the negative impacts of CH3Br usage pending the development of suitable replacement fumigants. [ABSTRACT FROM AUTHOR]

Although long-regarded as an excellent soil fumigant for killing plant pests, methyl bromide (MeBr) was phased out in 2005 in the USA, because it can deplete the stratospheric ozone layer. Iodomethane (Mel) has been identified as an effective alternative to MeBr and is used in a number of countries for preplant pest control. However, MeI is highly volatile and potentially carcinogenic to humans if inhaled. In addition, iodide anions, a breakdown product of Mel, can build up in fumigated soils and potentially cause plant toxicity and contaminate groundwater via leaching. In order to overcome the above two obstacles in MeI application, a method is proposed to place reactive bags containing ammonium hydroxide solution (NH4OH) on the soil surface underneath an impermeable plastic film covering the fumigated area. Our research showed that using this approach, over 99% of the applied MeI was quantitatively transferred to iodide. Of all the resulting iodide, only 2.7% remained in the fumigated soil, and 973% was contained in the reactive bag that can be easily removed after fumigation. [ABSTRACT FROM AUTHOR]

Transient infrared absorption spectroscopymonitors condensed-phasephotodissociation dynamics of 30 mM CHBr3and 50 mM CHI3in liquid CCl4. The experiments have picosecondtime resolution and monitor the C–H stretch region of boththe parent polyhalomethanes and their photolytically generated isomers.The C–H stretching transitions of these isomers, in which theemergent halogen atom returns to form a C–X–X bondingmotif, appear about 9 ps after photolysis for iso-CHBr2–Br and in about 46 ps for iso-CHI2–I. These time scales are consistent with,but differ from, the time evolution of the transient electronic absorptionspectra of the same samples, highlighting the subtle differences betweenmonitoring the vibrational and electronic chromophores. The specificityof using vibrational transitions to track condensed-phase reactiondynamics permits reassessment of the transient electronic spectrumof photolysis in neat CHBr3, which has an additional promptfeature near 400 nm. Calculations show that this feature, which arisesfrom a precursor to the isomer, is a charge-transfer transition ofa contact pair between the nascent Br fragment and a nearby CHBr3molecule. Dilution and solvent studies show that transitionis independent of the solvent. The iso-CHBr2–Br transition wavelength, however, shifts over the rangeof 400 to 510 nm depending on the solvent. Time-dependent densityfunctional calculations faithfully reproduce these trends. [ABSTRACT FROM AUTHOR]

Oxidation mechanisms in air nonthermal plasma (NTP) at room temperature and atmospheric pressure were investigated in a corona reactor energized by +dc, -dc, or +pulsed high voltage.. The two bromomethanes CF2Br2 and CH2Br2 were chosen as model organic pollutants because of their very different reactivities with OH radicals. Thus, they served as useful mechanistic probes: they respond differently to the presence of humidity in the air and give different products. By FT-IR analysis of the postdischarge gas the following products were detected and quantified: CO2 and CO in the case of CH2Br2, CO2 and F2C-O in the case of CF2Br2. F2C-O is a long-lived oxidation intermediate due to its low reactivity with atmospheric radicals. It is however removed from the NTP processed gas by passage through a water scrubber resulting in hydrolysis to CO2 and HF. Other noncarbon containing products of the discharge were also monitored by FT-IR analysis, including HNO3 and N2O. Ozone, an important product of air NTP, was never detected in experiments with CF2Br2 and CH2Br2 because of the highly efficient ozone depleting cycles catalyzed by BrOx species formed from the bromomethanes. It is concluded that, regardless of the type of corona applied, CF2Br2 reacts in air NTP via a common intermediate, the CF2Br radical. The possible reactions leading to this radical are discussed, including, for -dc activation, charge exchange with O2-, a species detected by APCI mass spectrometry. [ABSTRACT FROM AUTHOR]

Tarping fumigated fields with low permeability films such as commercial Totally Impermeable Film (TIF) can significantly reduce emissions, but it can also increase fumigant residence time in the soil such that extended tarp- covering durations may be required to address potential exposure risks during tarp-cutting and removal. In an effort to develop safe practices for using TIF, a large field study was conducted in the San Joaquin Valley of California. Comprehensive data on emissions (measured with dynamic flux chambers), fate, and transport of 1,3-dichloropropene and chloropicrin were collected in a 3.3 ha field fumigated with Pic-Clor 60 via broadcast shank application. Low emission flux (below 15 μg m-2 s-1) was observed from the tarped field throughout the tarp-covering period of 16 days with total emission loss of <8% of total applied for both chemicals. Although substantially higher flux was measured at tarp edges (up to 440 μg m-2 s-1), the flux was reduced to below 0.5 μg m-2 s-1 beyond 2 m of tarp edge where total mass loss was estimated to be =1% of total applied to the field. Emission flux increased following tarp-cutting, but was much lower compared to 5 or 6 d tarp-covering periods determined in other fields. This study demonstrated the ability of TIF to significantly reduce fumigant emissions with supporting data on fumigant movement in soil. Proper management on use of the tarp, such as extending tarp-covering period, can reduce negative impact on the environment and help maintain the beneficial use of soil fumigants for agricultural productions. [ABSTRACT FROM AUTHOR]

The rate constants of the H-abstraction reactions fromCH3Cl and CH3Br molecules by ClO and BrO radicalshave beenestimated over the temperature range of 300–2500 K using fourdifferent levels of theory. Calculations of optimized geometricalparameters and vibrational frequencies are performed using B3LYP andMP2 methods combined with the cc-pVTZ basis set. Single-point energycalculations have been carried out with the highly correlated ab initiocoupled cluster method in the space of single, double, and triple(perturbatively) electron excitations CCSD(T) using the cc-pVTZ andcc-pVQZ basis sets. Canonical transition-state theory combined withan Eckart tunneling correction has been used to predict the rate constantsas a function of temperature. In order to choose the appropriate levelsof theory with chlorine- and bromine-containing species, the referencereaction Cl (2P3/2) + CH3Cl →HCl + CH2Cl (Rref) was first theoretically studiedbecause its kinetic parameters are well-established from numerousexperiments, evaluation data, and theoretical studies. The kineticparameters of the reaction Rrefhave been determined accuratelyusing the CCSD(T)/cc-pVQZ//MP2/cc-pVTZ level of theory. This levelof theory has been used for the rate constant estimation of the reactionsClO + CH3Cl (R1), ClO + CH3Br (R2), BrO + CH3Cl (R3), and BrO + CH3Br (R4). Six-parameter Arrhenius expressions havebeen obtained by fitting to the computed rate constants of these fourreactions (including cis and trans pathways) over the temperaturerange of 300–2500 K. [ABSTRACT FROM AUTHOR]

Surface topography is here investigated as a route tocontrollingcrystal nucleation. The nucleation from vapor of crystals of neo-pentanol and tetrabromomethane was studied on flat surfacesof glass and mica, and on identical substrates scratched with diamondpowders of varying particle size. The result is a study which presentsa systematic comparison of the nucleating ability of surfaces withthe same chemistry and wettability, but varying surface topography.An increase in nucleation density of up to an order of magnitude wasobserved on scratched mica surfaces compared to unscratched ones,and there was a decrease in the induction time by up to 60%. Largerdiamond particles led to enhanced effects, particularly on the nucleationdensity. Although the nucleation density and induction time on unscratchedglass were similar to those on mica, the surface scratches on glasshad no significant effect on nucleation density or induction time.The results suggest that a high density of nanoscale features of thesurface topography, such as those produced as the diamond particlesfracture the mica, is necessary for an enhancement of nucleation.The apparent length scale of the topographical features on mica isdiscussed with reference to classical nucleation theory and othermodels. These results show that both a quantitative reduction in inductiontime and an increase in nucleation density can be achieved as a resultof mechanically produced topographical surface defects, which suggeststhat the engineering of nanoscale topographical features has realpotential for control of heterogeneous nucleation. [ABSTRACT FROM AUTHOR]

Bare metal anions K-, Rb-, Cs-, Fe-, Co-, Ni-, Cu-, and Ag-, generated by electrospray ionization of the corresponding oxalate or tricarballylate solutions, were allowed to react with methyl and ethyl chloride, methyl bromide, nitromethane, and acetonitrile in the collision hexapole of a triple-quadrupole mass spectrometer. Observed reactions include (a) the formation of halide, nitride, and cyanide anions, which was shown to be likely due to the insertion of the metal into the C-X, C-N, and C-C bonds, (b) transfer of H+ from the organic molecule, which is demonstrated to most likely be due to the simple transfer of a proton to form neutral metal hydride, and (c) in the case of nitromethane, direct electron transfer to form the nitromethane radical anion. Interestingly, Co- was the only metal anion to transfer an electron to acetonitrile. Differences in the reactions are related to the differences in electron affinity of the metals and the ΔacidH° of the metals and organic substrates. Density functional theory calculations at the B3-LYP/6-311++G(3df,2p)//B3-LYP/6-31+G(d) level of theory shed light on the relative energetics of these processes and the mechanisms by which they take place. [ABSTRACT FROM AUTHOR]

We describe the dissociative attachment (DA) of methyl bromide to form chemisorbed CH3 and Br on a Si(100)-2×1 surface at 270 K. The patterns of DA were studied experimentally by ultra-high vacuum scanning tunneling microscopy (STM) and interpreted by ab initio theory. The parent molecules were found to dissociate thermally by breaking the C-Br bond, attaching the resulting fragments CH3 and Br at adjacent Si-atom sites. The observed DA resulted in three distinct attachment geometries: inter-row (IR, 88%), inter-dimer (ID, 11%), and on-dimer (OD, 1%). Ab initio computation agreed in predicting these three DA reaction pathways, with yields decreasing down the series, in accord with experiment. The three computed physisorption geometries, each of which correlated with a preferred outcome, IR, ID, or OD, exhibited similar heats of adsorption, the choice of pathway being governed by the energy barriers to DA chemisorption predicted to increase along the series: EIR = 0.48 eV, EID = 0.57 eV, and EOD = 0.63 eV. [ABSTRACT FROM AUTHOR]

Two different synthetic routes for the preparation of 5,10,15-triaryl-tetrabenzocorroles have been developed. The first approach is based on the condensation of a tetrahydroisoindole with aryl-aldehydes, and the second pathway involves a cross-coupling reaction between a bromo-substituted corrole and a suitable substrate to form the four β-fused aryl rings. These routes are successful to lead to the target tetrabenzocorroles, obtained in both cases as the corresponding Cu complex and with the highest yield obtained via the one-step cross-coupling methodology. Demetalation of the Cu-tetrabenzocorrole produces the corresponding free base; this macrocycle was further exploited to obtain the Sn and Co complexes in good yields. [ABSTRACT FROM AUTHOR]

Emissions of methyl bromide (MeBr) from agricultural fumigation can lead to depletion of the stratospheric ozone layer, and so its use is being phased out. However, as MeBr is still widely used under Critical Use Exemptions, strategies are still required to control such emissions. In this work, novel reactive films (REs) were designed and their, efficacy in limiting loss of MeBr from soil was tested. A reactive layer, containing dry ammonium thiosulfate (ATS), was sandwiched between two layers of plastic film, the lower layer being HDPE (high-density polyethylene film, which is permeable to MeBr) and the upper layer HDPE or VIF (virtually impermeable film). MeBr diffusion through, and transformation by, the RFs were tested in a stainless-steel permeability cell. Although ineffective when dry, the RFs substantially depleted MeBr when activated with water to produce ATS solution. MeBr half-life (t1/2) was around 9.0 h at 20 °C in the presence of activated RF, and was sensitive to temperature (t1/2 15.7 and 2.9 h at 10 and 40 °C, respectively). When the upper film layer was VIF, less than 0.15% of the added MeBr diffused through the film, with the remainder being transformed within the reactive layer. These findings indicate that such films have good potential to reduce MeBr loss from fumigated soils to the atmosphere. [ABSTRACT FROM AUTHOR]

Despite generally being considered the most effective soil fumigant, methyl bromide (MeBr) use is being phased out because its emissions from soil can lead to stratospheric ozone depletion. However, a large amount is still currently used due to Critical Use Exemptions. As strategies for reducing the postfumigation emissions of MeBr from soil, Ca(OH)2, K2CO3, and NH3 were assessed as means of promoting MeBr degradation. Ammonia aqueous solution (NH4OH) was the most effective, because MeBr can be degraded by both hydrolysis and ammonolysis. At 20 °C, the half-lives (t1/2) of MeBr were 18.0, 2.5, and 1.3 h in 0.1, 1.0, and 2.0 M NH4OH, respectively. In 1.0 M NH4OH, increasing the solution temperature to 40 °C reduced the half-life of MeBr to 0.23 h. Ammonia amendment to moist soil also promoted MeBr transformation, and the MeBr degradation rate increased with increasing soil temperature. NH4OH (30%, 16 M) very effectively reacted with MeBr that was contained under plastic film. Under Hytibar (a virtually impermeable film, VIF), over 99.5% of the MeBr could be destroyed by 30% NH4OH in 8 h at 20 °C. On the basis of these results, good management practices (i.e., VIF plus NH4OH) could be developed for continued use of MeBr as a soil fumigant under Critical Use Exemptions, without significant emissions. [ABSTRACT FROM AUTHOR]

For the recovery and purification of proteins, an amphoteric hollow-fiber membrane (AHFM) was prepared from bromomethylated poly(2,6-dimethyl-1,4-phenylene oxide) (BPPO) by ethylenediamination and carboxylation. The success in modifying BPPO was confirmed by FTIR spectra, amphoteric group density, anion-exchange capacity (AEC), and cation-exchange capacity (CEC). For potential applications, the membranes were tested for the adsorption of lysozyme, and the results showed that the adsorption amount increased with increasing initial lysozyme concentration. The adsorption fits the Langmuir isotherm and the Freundlich equation well, and the maximum experimental amount of lysozyme adsorbed was found to be 4.00 mg/g, which was close to the calculated values (3.85 and 4.13 mg/g according to the Langmuir and Freundlich equations, respectively). [ABSTRACT FROM AUTHOR]

A series of heterdepth tedentate ruttreriurn(t) satiplexes of composition [(H2bzim)Ru(tpy-X](PF6)2 (1-7), where H2pbbzim = 2,6-bis(benzimidazoIe-2-yl) pyridine and tpy-X = 4-substituted terpyridine ligands with X = H, p-triphenyl-phosphonium methyl bromide (PhCH3), p-bromomrnthypenylm bromide (PhCH2Br),pdibromenthylpherryl (PFCHBr2pcyanomethylphenyl (PhCH2CN),p-triphenyl phesphonhim methyiphenyf brcmkb (PhCH2PPh3Br), and 4'-phenylform',I (PhCHO) groups, has been synthesized and deamoterized by using standard analytic and spentrvscopctethniquea These anspounda were designed to huease the exofted-state Iifetime of ruthenium(II) bisterpyridine-type complexes. The X-ray crystal structure of a representative sanpound 2, which crystalized with morro spoon grarp P2(1)/c; has been determined. The absorption spectra, redox behavior, and luminance properties of the ruthenkrm(ll) complexes have been thoroughly investigated. All of the complexes display moderately strong luminance at room temperature with lifetime wiht the range of 10-58 ns. Correlations have been obtained for the Harmett σp ,parameter with their MLCT emission energies, Iifetimes, redox potentials, proton NMR chemical shifts, tec. The anion binding properties of at the complexes as well as the parent ligend H2pbbzim have been studied in acetonitr using absorption, emission, and 1H NMR spectral studies, and it has been observed that the metatoreceptors act as sensors for F, AC, and to sane extent H2PO4. At a relatively loner concentraton of anions, al:t H-bonded addict is formed; however, in the presence of an excess of anions, stepwise deprotorsettun of the two benztnidazofe N-H fragments occurs, an event whid'r is signaled by the development of vivid colors visible with the naked eye. The receptor-action binding constants have been evaluated. Q,do vottammetle (CV) measurements carried or lea acetonitrile-dimenthylformamide (9:1) provided in favor of an ion(F, AC) concentration dependent etectroctremical responses, enabling 1 -7 to act as suitable electrochemical sensors for F and AcO ions. [ABSTRACT FROM AUTHOR]

The reaction of 1,2,4,5-tetrakis(bromomethyl)benzene and hexakis(bromomethyl)benzene with the alkoxide of 2,2-bis(1-pyrazolyl)ethanol leads to the synthesis of the new polytopic ligands 1 ,2,4,5-C6H2[CH2OCH2CH(pz)2]4 (Ltetra, pz a pyrazolyl ring) and C6[CH2OCH2CH(pz)2]6 (Lhexa). Reactions of these ligands and the appropriate silver(l) salt lead to the preparation of [Ag2Ltetra](BF4)2 (1), [Ag2Ltetra](SO3CF3)2 (2), [Ag3Lhexa](BF4)3 (3), and [Ag3Lhexa](ClO4)3 (4). The solid-state structures of tour different complexes crystallized from solutions of 1 or 2 yield five independent structures of the [Ag2Ltetra]2+ cation, all with similar structures. In all of the structures, two para-oriented pairs of "arms" (-CH2OCH2CH(pz)2) from a single ligand each chelate a silver(l) ion on the opposite sides of the atone ring, forming a double, mononuclear metallacyclic structure of two 17-membered rings connected by the central arene ring. The structures about the silver(l) cations in these complexes are distorted tetrahedral, The flexibility of the ligand leads to two types of arrangements of the linking arms in the five complexes. The central cations of the two Lhexa complexes also form double, mononuclear metallacycles, but the structures are different from those of the silver complexes of Ltetra in that both Lhexa cations contain one para-linked and one meta-linked metallacycle, thus forming a 16- and a 17-membered ring. In addition, the two remaining arms on Lhexa coordinate with additional silver(l) cations, linking the double, mononuclear metallacyctes into a coordination polymer network. [ABSTRACT FROM AUTHOR]

The influence of the physicochemical properties of the vesicular bilayer on the sorption of poorly water soluble compounds was investigated with pulsed field gradient 1H nuclear magnetic resonance (PFG-NMR) for the case of phosphatidylcholine and dioctadecyldimethylammonium bromide (DODAB), using 4-ethylbenzyl alcohol as a model compound. Hereby, the effect of bilayer thickness at a constant physicochemical state was studied using a range of phosphatidylcholines of varying chain lengths, whereas DODAB was preferred to check the influence of the bilayer physicochemical state since this cationic lipid is characterized by three different states within the studied temperature range. When the phospholipid alkyl chain length was changed, no differences were observed in the sorption which was linked to the surface-mediated sorption. On the other hand, when the chemical composition was preserved but the temperature and thus the physical state of the bilayer were changed, the sorption in dioctadecyldimethylammonium bromide (DODAB) vesicles changed dramatically. From those experiments, a strong relationship between the ordering of the surfactant molecules and the sorption can be assumed. [ABSTRACT FROM AUTHOR]

5-Alkoxymethyl-2-aryl-3-fluoro-1H-pyrroles and 2-aryl-3- fluoro-1H-pyrrole-5-carbaldehydes were efficiently prepared from the corresponding 2-aryl-5-(bromomethyl)- 1H-pyrrolines via electrophilic α,α-difluorination of the imino bond, using Selectfluor (1-chloromethyl-4-fluoro-1,4-diazoniabicyclo- [2.2.2]octane bistetrafluoroborate) and subsequent aromatization by dehydrofluorination. This methodology provides a new and easy entry toward various new 3-fluorinated pyrroles. [ABSTRACT FROM AUTHOR]

Methyl bromide (CH3Br) is the most abundant brominated organic compound in the atmosphere. It is known to originate from natural and anthropogenic sources, although many uncertainties remain regarding strengths of both sources and sinks and the processes leading to its formation. In this study a potential new CH3Br source from vegetation has been examined, analogous to the recently discovered abiotic formation of methyl chloride from plant pectin. Several plant samples with known bromine content, including ash (Fraxinus excelsior), saltwort (Batis maritima), tomato reference material (NIST-1573a), hay reference material (IAEA V-10), and also bromine enriched pectin, were incubated in the temperature range of 25-50 °C and analyzed for CH3Br emission using gas chromatography/mass spectrometry. All plant samples inspected showed an exponential increase in CH3Br emission as a function of temperature increase,i.e., emissions were observed to approximately double with every 5 °C rise in temperature. Next to temperature, it was found that emissions of CH3Br were also dependent on the bromine content of the plants. The highest CH3Br release rates were found for the saitwort which contained the highest bromine concentration. Arrhenius plots confirmed that the observed emissions were from an abiotic origin. The contribution of abiotic CH3Br formation from vegetation to the global budget will vary geographically as a result of regional differences in both temperature and bromide content of terrestrial plants. [ABSTRACT FROM AUTHOR]

The vacuum ultraviolet laser-excited photoion-pair formation spectrum of CH 3Br has been measured under high resolution in the threshold region. The (2 + 1) and (3 + 1) resonance-enhanced multiphoton ionization spectra in the same energy region are also reported. By comparison of the spectra in this and a more extended region, resonances in the photoion-pair formation spectrum are assigned to p and f Rydberg states. It is concluded that all the structure in the photoion-pair formation spectrum near threshold can be accounted for by members of the Ω = 0 subset of Rydberg states that act as doorway states to the ion channel. [ABSTRACT FROM AUTHOR]

Methyl chloride (CH3Cl) and methyl bromide (CH3Br) are both produced and consumed by terrestrial ecosystems, but large uncertainties remain about the magnitude of their emission and uptake rates. Most field-based studies report net fluxes, but knowledge of gross fluxes is required to assess partial atmospheric lifetimes and potential mechanisms. Here, we present the first field results using a stable isotope tracer technique to determine gross emission and uptake fluxes of CH3Cl and CH3Br at two temperate annual grasslands in California. These grasslands generally showed modest emission and uptake rates of CH3Cl and CH3Br, although large net emissions were observed at riparian and dry playa sites within these grasslands. While gross production rates of the methyl halides are not correlated to each other, gross consumption rates of CH3Cl and CH3Br show a molar uptake ratio of ~40:1, consistent with results from other biomes. Gross consumption rates appear to be strongly affected by soil moisture. Temperate grassland soils have been previously identified as a globally significant sink for CH3Br, accounting for approximately 25% of the total soil sink, but our results suggest that the uptake rate could be much smaller. [ABSTRACT FROM AUTHOR]

endo-3-Diazotricyclo[3.2.1.02,4]oct-6-ene (endo-6) has already been prepared in solution. According to B3LYP/6-311 +G(d,p) computations, the corresponding carbene endo-7 easily produces the highly strained neutral C8H8 compound 4 comprising a pyramidally tetracoordinated carbon which then rearranges to bridgehead alkene 15 through a cascade of rearrangements. Nonplanar diazocyclopropane structures are predicted for endo- and exo-6. Furthermore, their ring-opened isomers 27 are the first representatives of a new class of non-Kekulé compounds, the diazoallyls. [ABSTRACT FROM AUTHOR]

Phase equilibria involving orientationally disordered (OD) and liquid phases of the two-component system between carbon tetrachloride (CCl4) and 2-methyl-2-bromomethane ((CH3)3CBr) have been determined by means of X-ray powder diffraction and thermal analysis techniques from 210 K up to the liquid state. The isomorphism relation between the OD stable face-centered cubic (FCC) phase of (CH3)3CBr and the metastable FCC phase of CCl4has been demonstrated throughout the continuous evolution of the lattice parameters and the existence of the two-phase equilibrium FCC L for the whole range of composition, despite the monotropy of the FCC phase for the CCl4component with respect to its OD rhombohedral (R) stable phase. A continuous series of OD R mixed crystals is found, which confirms the R lattice symmetry of the OD phase II of (CH3)3CBr, for which the crystallographic results have been long-time misinterpreted. X-ray patterns of such a phase were indexed according to the recent single-crystal results obtained by Rudman (Rudman, R. J. Mol. Struct.2001, 569, 157). In addition, some experimental evidences are given to confirm the number of molecules per unit cell (Z 21). The thermodynamic assessment reproduces coherently the phase diagram for the stable R L and R FCC two-phase equilibria as well as for the partially metastable FCC L two-phase equilibrium and provides a set of data for the thermodynamic properties of nonexperimentally available phase transitions of pure components. Surprisingly, the phase equilibrium involving R and FCC OD phases appears as one of the very few showing a solid−solid equilibrium with two extremes. [ABSTRACT FROM AUTHOR]

Laser-ablated thorium atoms react with methyl fluoride to give the CH2=ThHF molecule as the major product observed and trapped in solid argon. Infrared spectroscopy, isotopic substitution, and density functional theoretical frequency calculations confirm the identification of this methylidene complex. The four strongest computed absorptions (Th-H stretch, Th=C stretch, CH2 wag, and Th-F stretch) are the four vibrational modes observed. The CH2=ThHCl and CH2=ThHBr species formed from methyl chloride and methyl bromide exhibit the first three of these modes in the infrared spectra. The computed structures (B3LYP and CCSD) show considerable agostic interaction, similar to that observed for the Group 4 CH2=MHX (M = Ti, Zr, Hf) methylidene complexes, and the agostic angle and C=Th bond length decrease slightly in the CH2=ThHX series (X = F, Cl, Br). [ABSTRACT FROM AUTHOR]

Bromomethane−water 1:2 complexes have been theoretically studied to reveal the role of hydrogen bond and halogen bond in the formation of different aggregations. Four stable structures exist on the potential energy surface of the CH3Br(H2O)2 complex. The bromine atom acts mainly as proton acceptor in the four studied structures. It is also capable of participating in the formation of the halogen bond. The properties and characteristics of the hydrogen bond and the halogen bond are investigated employing several different quantum chemical analysis methods. Cooperative effects for the pure hydrogen bonds or the mixed hydrogen bonds with halogen bonds and the possibility of describing cooperative effects in terms of the topological analysis of the electronic density or the charge-transfer stabilization energy are discussed in detail. An atoms-in-molecules study of the hydrogen bond or the halogen bond in the bromomethane−water 1:2 complexes suggests that the electronic density topology of the hydrogen bond or the halogen bond is insensitive to the cooperative effect. The charge-transfer stabilization energy is proportional to the cooperative effect, which indicates the donor−acceptor electron density transfer to be mainly responsible for the trimer nonadditive effect. [ABSTRACT FROM AUTHOR]

A new methodology for bromine stable isotope determination by continuous-flow isotope ratio mass spectrometry (CF-IRMS) was developed. The technique was tested on inorganic samples. Inorganic bromide was precipitated in the form of silver bromide by using silver nitrate in a standard methodology. Bromine stable isotope analysis was carried out on methyl bromide (CH3Br) after converting silver bromide to methyl bromide by reacting it with methyl iodide (CH3I). The system used in this study is an IsoPrime IRMS, with analytical capabilities of both dual-inlet and continuous-flow modes coupled with an Agilent 6890 GC equipped with a CTC Analytics Combi- PAL autosampler. This new technique measures samples as small as 0.2 mg of AgBr (1 μmol of Br-). The bromine stable isotope analysis using continuous flow technology showed excellent precision and accuracy. The internal precision using pure methyl bromide gas is better than ±0.03‰ (±SD); the external precision using seawater standard is better than ±0.06‰ (±SD) for n = 12. Moreover, the sample analysis time is 16 min, as compared to 75 mm needed in previous techniques. This allows for 50 samples to be analyzed in 1 day, as compared to 8 samples using the conventional techniques. A series of natural saline formation waters and brines from sedimentary and crystalline rock environments was measured by this new methodology to test the potential natural range of δ81Br. The bromine isotopic composition of the samples ranged from 0.00 to +1.80‰ relative to standard mean ocean bromide (SMOB). Initial trends and distinctive isotopic difference were noticed between crystalline shield brines and sedimentary formation brines. [ABSTRACT FROM AUTHOR]

A computational study of the oxidation of CH2Br2 and CHBr3 initiated via both UV photolysis and abstraction of an H atom by OH/Cl radicals has been performed. We have calculated the energetics associated with the addition of O2 to the substituted bromomethyl radicals and the subsequent addition of NO to the peroxy radicals to form energized peroxy nitrite molecules. The peroxy nitrite molecules are predicted to dissociate rapidly to form alkoxy radicals (CH2BrO and CHBr2O) and NO2, and the kinetics of these reactions have been determined using Rice-Ramsperger-Kassel-Marcus/master equation calculations. We additionally find that the reaction of the peroxy radicals with HO2 may directly lead to significant production of alkoxy radicals, a pathway that is unimportant in nonbrominated analogues. We predict that the alkoxy radicals will dissociate rapidly via C-Br bond cleavage. The atmospheric implications of these results will be discussed. [ABSTRACT FROM AUTHOR]

We have performed photodissociation experiments on CHBr3 at 248 nm using VUV ionization photofragment translational spectroscopy. Prompt C-Br bond fission is the dominant single-photon dissociation channel. In addition to primary Br and CHBr2 signals, we observe Br, CHBr, CBr, HBr, and Br2 products attributed to secondary photodissociation of CHBr2 and CHBr. There are three competing fragmentation channels from the photodissociation of CHBr2: CHBr + Br, CH + Br2, and CBr + HBr. The conclusion that Br2 fragments do not arise from a single-photon channel in appreciable yield is supported by transient FM absorption measurements of the CHBr radical. Because the molecular HBr and Br2 detachment channels are multiphoton processes, they will have very little impact on the atmospheric chemistry of CHBr3. We conclude that the most important photodissociation channel of CHBr3 in the UV region is C-Br bond breaking. [ABSTRACT FROM AUTHOR]

Use of methyl bromide (MeBr) as a quarantine, commodity, or structural fumigant is under scrutiny because its release to the atmosphere contributes to the depletion of stratospheric ozone. A closed-system bioreactor consisting of 0.5 L of a growing culture of a previously described bacterium, strain IMB-1, removed MeBr (>110 µmol L[sup -1]) from recirculating air. Strain IMB-1 grew slowly to high cell densities in the bioreactor using MeBr as its sole carbon and energy source. Bacterial oxidation of MeBr produced CO[sub 2] and hydrobromic acid (HBr), which required continuous neutralization with NaOH for the system to operate effectively. Strain IMB-1 was capable of sustained oxidation of large amounts of MeBr (170 mmol in 46 d). In an opensystem bioreactor (10-L fermenter), strain IMB-1 oxidized a continuous supply of MeBr (220 µmol L[sup -1] in air). Growth was continuous, and 0.5 mol of MeBr was removed from the air supply in 14 d. The specific rate of MeBr oxidation was 7 × 10[sup -16] mol cell[sup -1] h[sup -1]. Bioreactors such as these can therefore be used to remove large quantities of contaminant MeBr, which opens the possibility of biodegradation as a practical means for its disposal. [ABSTRACT FROM AUTHOR]

Examines the interaction between methyl bromide and soil. Degradation of methyl bromide in soils; Assessment on the chemical structures of separated soil fractions; Reduction of methyl bromide after soil fumigation.

Presents a method for estimating the mass transfer coefficient of fumigant vapors across agricultural films. Permeability of plastic films to gaseous solutes; Environmental impact of methyl bromide and other soil fumigants; Advantages of the method; Diffusion of methyl bromide, propargyl bromide and chloropicrin through 1-mil high-density polyethylene.

Describes a novel method for collecting methyl bromide (MeBR) from farm fields where MeBr has been applied. Schematic of the double layer collection system; Potential applications in field fumigation and for mitigating MeBr emissions.

Studies the use of a plasticized poly(vinyl chloride) optode membrane as a reversible sensing device for the indirect optical determination of nicotine. Extraction of nicotine and conversion to its bromoethane derivative; Extraction of the quaternary ammonium ion; Response behavior of different membrane formulations.

Presents a study where organic waste was applied to reduce the emission of methyl bromide and methyl isothiocyanate, by enhancement of their degradation in surface soil. Acceleration of the degradation of both compounds in composted manure of biosolid-manure amended soils; Indication of the difference in degradation kinetics between sterile and nonsterile amended soil.

Examines the toxicological effects of emissions of methyl bromide from soil fumigation on stratospheric ozone depletion and humans. Role of methyl bromide in the control of soil-borne diseases; Details on studies conducted on methyl bromide; Possible effects of an excessive emission of methyl bromide.

Focuses on field studies conducted in California which indicate that methyl bromide used in soil fumigation is lost to atmospheric emission when the fields are covered completely with a high-density polyethylene (HDPE) film. Methods used to conduct studies on bromide emissions; Effects of methyl bromide on the environment; Reference to some of the chemicals used in agricultural soil fumigation.

Presents a study which looks at effectiveness of a high-barrier plastic film, Hyibar, for reducing methyl bromide emission with replicates field plots. Detailed information on the methodology used to conduct the study; Discussion surrounding the results of the study.

Presents a study which looks at the reduction of methyl bromide emission through the use of field management practices. Effectiveness of methyl bromide as a soil fumigant; Details on experiments; Results of the study.

Studies the oxidation of methyl bromide (MeBr) in the water column of Mono Lake, California. Measurement of the formation of H14CO3 from [14C]MeBr; Field studies; Chemical degradation of MeBr.

Reports on the environmental fate and transport of methyl bromide (MeBr) in an agricultural field after deep injection. Use of independent methods to estimate the total MeBr lost after application; Factors attributing to the discrepancy in the bromine and direct flux measurements; Impact of deep injection on methyl bromide emissions.

Examines the stimulation of microbial degradation of methyl bromide in soil during oxidation of an ammonia fertilizers by nitrifiers. Involvement of microbial and chemical degradation in the methyl bromide degradation in soil; Nitrosomonas europaea; Stimulation of methyl bromide degradation through liming and application of an ammonia fertilizer.

Presents a study on the effect of soil factors of methyl bromide volatilisation (MeBr). Where volatilisation of MeBr occurs; Variations in methyl bromide volatilisation rates; Effects of applying MeBR at a shallow depth; Information on the experimental procedures used in study; Results and discussion of study.

Determines the feasibility of gravimetrically preparing gas standards containing methyl bromide at the 5-60 parts per trillion level. Experimental procedure; Intercomparison of primary gravimetric standards; Determination of methyl bromide in air samples taken from Niwot Ridge, Colorado.

Details a study on cavitands prepared in 29 to 90 percent yield by bridging of the chair-methylresorcin[4]arenes with bromochloromethane. Review of related literature; Results and discussions; Experimental methods.

Presents chemical research on methyl bromide to understand the natural sinks and ambient mixing ratios of this compound. Theory; Methodology; Results and discussion.

The article describes the formation of a nickel-methyl species when methyl-coenzyme M reductase (MCRred1a) state is incubated with bromomethane (BrMe). According to the authors, incubation of MCRred1a results in the loss of the electron paramagnetic resonance signal of the species and the formation of an electron paramagnetic resonance signal designated MCRBrMe. The characterization of electronic and geometric structure of MCRBrMe is provided.

Despite a phaseout slated for 2005, farmers in several industrialized countries can continue to use the agricultural pesticide methyl bromide, which is known to damage the stratospheric ozone layer. Eleven countries garnered limited critical-use exemptions for 2005, which total 13,400 metric tons, under a compromise agreement reached during the latest Montreal Protocol negotiations that concluded in Montreal, Quebec, in late March. Further exemption requests are now being considered for 2006 and beyond. Under the original Montreal Protocol, developed countries reduced their methyl bromide use to 30% of their 1991 baseline levels.

Reports on companies in the United States and Canada's application for exemptions from the 2005 phaseout date of the methyl bromide, a pesticide that depletes the stratospheric ozone layer. Reasons for the delay in the effort to replace methyl bromide; Canada's coordination with grain millers to adopt alternatives to methyl bromide; critical use criteria outlined by the Montreal Protocol to the Technology and Economic Assessment Panel of the United Nation's Ozone Secretariat.