Theoretical study of the reactions of CF3OCHF2 with the hydroxyl radical and the chlorine atom.

Theoretical investigations are carried out on the reaction mechanism of the reactions of CF3OCHF2 (HFOC-125) with the OH radials and Cl atoms, as well as the heats of formation of CF3OCHF2 and CF3OCF2. The electronic structure information on the potential energy surface for each reaction is obtained at the B3LYP/6-311G(d,p) level, and energetic information is further refined by G3(MP2) theory. The direct dynamics calculation of the hydrogen abstraction reactions are also performed at the G3(MP2)//B3LYP/ 6-311G(d,p) level. The classical energy profile is corrected by interpolated single-point energies (ISPE) approach, incorporating the small-curvature tunnelling effect (SCT) calculated by the variational transition-state theory (VTST). The rate constants are in good agreement with the experimental data and are found to be k1 = 4.95 x 10(-30)T(5.40)exp(-347/T) and k2 = 1.86 x 10(-23)T(3.43)exp(-1579/T) cm3 molecule(-1)s(-1) over the temperature range 200-2000 K. The rate constants at 298 K for these two reactions are 3.38 x 10(-16) and 2.80 x 10(-17) cm3 molecule(-1)s(-1), respectively. Using group-balanced isodesmic reactions as working chemical reactions, the standard enthalpies of formation for CF3OCHF2 and CF3OCF2 are -312.3 +/- 1.0 and -257.3 +/- 1.0 kcalmol(-1), respectively, evaluated by G3(MP2) theory based on the B3LYP/6-311G(d,p) geometries. The theoretical studies provide rate constants of the title reactions and the enthalpies of the species, which are important parameters in determining the atmospheric lifetime and the feasible pathways for the loss of HFOC-125.     

Experimental and ab initio dynamical investigations of the kinetics and intramolecular energy transfer mechanisms for the OH + 1,3-butadiene reaction between 263 and 423 K at low pressure

The rate constants for the reaction of the OH radical with 1,3-butadiene and its deuterated isotopomer has been measured at 1-6 Torr total pressure over the temperature range of 263-423 K using the discharge flow system coupled with resonance fluorescence/laser-induced fluorescence detection of OH. The measured rate constants for the OH + 1,3-butadiene and OH + 1,3-butadiene- d 6 reactions at room temperature were found to be (6.98 +/- 0.28) x 10 (-11) and (6.94 +/- 0.38) x 10 (-11) cm (3) molecule (-1) s (-1), respectively, in good agreement with previous measurements at higher pressures. An Arrhenius expression for this reaction was determined to be k 1 (II)( T) = (7.23 +/- 1.2) x10 (-11)exp[(664 +/- 49)/ T] cm (3) molecule (-1) s (-1) at 263-423 K. The reaction was found to be independent of pressure between 1 and 6 Torr and over the temperature range of 262- 423 K, in contrast to previous results for the OH + isoprene reaction under similar conditions. To help interpret these results, ab initio molecular dynamics results are presented where the intramolecular energy redistribution is analyzed for the product adducts formed in the OH + isoprene and OH + butadiene reactions.     

Kinetic and product study of the gas-phase reactions of OH radicals, NO(3) radicals, and O(3) with (C(2)H(5)O)(2)P(S)CH(3) and (C(2)H(5)O)(3)PS

Rate constants for the reactions of OH radicals and NO3 radicals with O,O-diethyl methylphosphonothioate [(C(2)H(5)O)(2)P(S)CH(3); DEMPT] and O,O,O-triethyl phosphorothioate [(C(2)H(5)O)(3)PS; TEPT] have been measured using relative rate methods at atmospheric pressure of air over the temperature range 296-348 K for the OH radical reactions and at 296 +/- 2 K for the NO(3) radical reactions. At 296 +/- 2 K, the rate constants obtained for the OH radical reactions (in units of 10(-11) cm(3) molecule(-1) s(-1)) were 20.4 +/- 0.8 and 7.92 +/- 0.27 for DEMPT and TEPT, respectively, and those for the NO(3) radical reactions (in units of 10(-15) cm(3) molecule(-1) s(-1)) were 2.01 +/- 0.20 and 1.03 +/- 0.10, respectively. Upper limits to the rate constants for the reactions of O(3) with DEMPT and TEPT of <6 x 10(-20) cm(3) molecule(-1) s(-1) were determined in each case. Rate constants for the OH radical reactions, measured relative to k(OH + alpha-pinene) = 1.21 x 10(-11) e(436/T) cm(3) molecule(-1) s(-1), resulted in the Arrhenius expressions k(OH + DEMPT) = 1.08 x 10(-11) e(871+/-25)/T cm(3) molecule(-1) s(-1) and k(OH + TEPT) = 8.21 x 10(-13) e(1353+/-49)/T cm(3) molecule(-1) s(-1) over the temperature range 296-348 K, where the indicated errors are two least-squares standard deviations and do not include the uncertainties in the reference rate constant. Diethyl methylphosphonate was identified and quantified from the OH radical and NO(3) radical reactions with DEMPT, with formation yields of 21 +/- 4%, independent of temperature, from the OH radical reaction and 62 +/- 11% from the NO(3) radical reaction at 296 +/- 2 K. Similarly, triethyl phosphate was identified and quantified from the OH radical and NO(3) radical reactions with TEPT, with formation yields of 56 +/- 9%, independent of temperature, from the OH radical reaction and 78 +/- 15% from the NO(3) radical reaction at 296 +/- 2 K.     

A kinetic study of the reactions of vanadium, iron, and cobalt with sulfur dioxide

A kinetic study of the reactions of ground state V, Fe, and Co with SO2 is reported. V, Fe, and Co were produced by the 248 nm photodissociation of VCl4, ferrocene, and Co(C5H5)(CO)2, respectively, and were detected by laser-induced fluorescence. V + SO2 proceeds by an abstraction reaction with rate constants given by k=(2.33 +/- 0.57)x 10(-10) exp[-(1.14 +/- 0.19) kcal mol(-1)/RT] cm3 molecule(-1) s(-1) over the temperature range 296-571 K. Fe + SO2 was studied in the N2 buffer range of 10-185 Torr between 294 and 498 K. The limiting, low-pressure third-order rate constants are given by k(0)=(3.45 +/- 1.19)x 10(-30) exp[-(2.81 +/- 0.24) kcal mol(-1)/RT] cm6 molecule(-2) s(-1). Co + SO2 was studied in the CO2 buffer range of 5-40 Torr between 294 and 498 K. This reaction is independent of temperature over the indicated range and has a third-order rate constant of k0=(5.23 +/- 0.28)x 10(-31) cm6 molecule(-2) s(-1). Results of this work are compared to previous work on the Sc, Ti, Cr, Mn, and Ni + SO2 systems. The reaction efficiencies for the abstraction reactions depend on the ionization energies of the transition metal atoms and on the reaction exothermicities, and the reaction efficiencies of the association reactions are strongly dependent on the energies needed to promote an electron from a 4s2 configuration to a 4s1 configuration.     

The d (3)Pi(g)-c (3)Sigma(u) (+) band system of C2

A two-dimensional fluorescence (excitation/emission) spectrum of C2 produced in an acetylene discharge was used to identify and separate emission bands from the d (3)Pi(g)<--c (3)Sigma(u) (+) and d (3)Pi(g)<--a (3)Pi(u) excitations. Rotationally resolved excitation spectra of the (4<--1), (5<--1), (5<--2), and (7<--3) bands in the d (3)Pi(g)<--c (3)Sigma(u) (+) system of C2 were observed by laser-induced fluorescence spectroscopy. The molecular constants of each vibrational level, determined from rotational analysis, were used to calculate the spectroscopic constants of the c (3)Sigma(u) (+) state. The principal molecular constants for the c (3)Sigma(u) (+) state are B(e)=1.9319(19) cm(-1), alpha(e)=0.018 55(69) cm(-1), omega(e)=2061.9 cm(-1), omega(e)x(e)=14.84 cm(-1), and T(0)(c-a)=8662.925(3) cm(-1). We report also the first experimental observations of dispersed fluorescence from the d (3)Pi(g) state to the c (3)Sigma(u) (+) state, namely, d (3)Pi(g)(v=3)-->c (3)Sigma(u) (+)(v=0,1).     

Free radical chemistry of disinfection-byproducts. 1. Kinetics of hydrated electron and hydroxyl radical reactions with halonitromethanes in water

Halonitromethanes are disinfection-byproducts formed during ozonation and chlorine/chloramine treatment of waters that contain bromide ion and natural organic matter. In this study, the chemical kinetics of the free-radical-induced degradations of a series of halonitromethanes were determined. Absolute rate constants for hydroxyl radical, *OH, and hydrated electron, e(aq)-, reaction with both chlorinated and brominated halonitromethanes were measured using the techniques of electron pulse radiolysis and transient absorption spectroscopy. The bimolecular rate constants obtained, k (M(-1) s(-1)), for e(aq)-/*OH, respectively, were the following: chloronitromethane (3.01 +/- 0.40) x 10(10)/(1.94 +/- 0.32) x 10(8); dichloronitromethane (3.21 +/- 0.17) x 10(10)/(5.12 +/- 0.77) x 10(8); bromonitromethane (3.13 +/- 0.06) x 10(10)/(8.36 +/- 0.57) x 10(7); dibromonitromethane (3.07 +/- 0.40) x 10(10)/(4.75 +/- 0.98) x 10(8); tribromonitromethane (2.29 +/- 0.39) x 10(10)/(3.25 +/- 0.67) x 10(8); bromochloronitromethane (2.93 +/- 0.47) x 10(10)/(4.2 +/- 1.1) x 10(8); bromodichloronitromethane (2.68 +/- 0.13) x 10(10)/(1.02 +/- 0.15) x 10(8); and dibromochloronitromethane (2.95 +/- 0.43) x 10(10) / (1.80 +/- 0.31) x 10(8) at room temperature and pH approximately 7. Comparison data were also obtained for hydroxyl radical reaction with bromoform (1.50 +/- 0.05) x 10(8), bromodichloromethane (7.11 +/- 0.26) x 10(7), and chlorodibromomethane (8.31 +/- 0.25) x 10(7) M(-1) s(-1), respectively. These rate constants are compared to recently obtained data for trichloronitromethane and bromonitromethane, as well as to other established literature data for analogous compounds.     

Quenching of I(2P1/2) by NO2, N2O4, and N2O

Quenching of excited iodine atoms (I(5p5, 2P1/2)) by nitrogen oxides are processes of relevance to discharge-driven oxygen iodine lasers. Rate constants at ambient and elevated temperatures (293-380 K) for quenching of I(2P1/2) atoms by NO2, N2O4, and N2O have been measured using time-resolved I(2P1/2) --> I(2P3/2) 1315 nm emission. The excited atoms were generated by pulsed laser photodissociation of CF3I at 248 nm. The rate constants for I(2P1/2) quenching by NO2 and N2O were found to be independent of temperature over the range examined with average values of (2.9 +/- 0.3) x 10(-15) and (1.4 +/- 0.1) x 10(-15) cm3 s(-1), respectively. The rate constant for quenching of I(2P1/2) by N2O4 was found to be (3.5 +/- 0.5) x 10(-13) cm3 s(-1) at ambient temperature.     

Lipid bilayers on polyacrylamide brushes for inclusion of membrane proteins

The ability of neutral polymer cushions to support neutral lipid bilayers for the incorporation of mobile transmembrane proteins was investigated. Polyacrylamide brush layers were grown on fused silica using atom-transfer radical polymerization to provide polymer layers of 2.5-, 5- and 10-nm thickness. Lipid bilayers composed of POPC (1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine) were formed by vesicle fusion onto bare fused silica and onto each of the polyacrylamide layers. Bilayer fluidity was assessed by the diffusion of a probe, NBD-labeled phosphatidylcholine, using fluorescence recovery after photobleaching. A transmembrane protein, the human delta-opioid receptor, was inserted into each lipid bilayer, and its ability to bind a synthetic ligand, DPDPE, cyclic[2-d-penicillamine, 5-d-penicillamine]enkephalin, was detected using single-molecule fluorescence spectroscopy by labeling this ligand with a rhodamine dye. The transmembrane protein was observed to bind the ligand for all bilayers tested. The protein's electrophoretic mobility was probed by monitoring the fluorescence from the bound ligand. The 5-nm polyacrylamide thickness gave the fastest diffusion for the fluorescent lipid probe (D(1) = 2.0(+/-1.2) x 10(-7) and D(2) = 1.2(+/-0.5) x 10(-6) cm(2)/s) and also the largest electrophoretic mobility for the transmembrane protein (3 x 10(-8) cm(2)/V.s). The optimum in polymer thickness is suggested to be a tradeoff between decoupling from the substrate and increasing roughness of the polymer surface.     

Experimental and theoretical studies of the kinetics of the reactions of OH and OD with 2-methyl-3-buten-2-ol between 300 and 415 K at low pressure

The rate constants for the reactions of OH and OD with 2-methyl-3-buten-2-ol (MBO) have been measured at 2, 3, and 5 Torr total pressure over the temperature range 300-415 K using a discharge-flow system coupled with laser induced fluorescence detection of OH. The measured rate constants at room temperature and 5 Torr for the OH + MBO reaction in the presence of O2 and the OD + MBO reaction are (6.32 +/- 0.27) and (6.61 +/- 0.66) x 10(-11) cm3 molecule(-1) s(-1), respectively, in agreement with previous measurements at higher pressures. However, the rate constants begin to show a pressure dependence at temperatures above 335 K. An Arrhenius expression of k0 = (2.5 +/- 7.4) x 10(-32) exp[(4150 +/- 1150)/T] cm6 molecule(-2) s(-1) was obtained for the low-pressure-limiting rate constant for the OH + MBO reaction in the presence of oxygen. Theoretical calculations of the energetics of the OH + MBO reaction suggest that the stability of the different HO-MBO adducts are similar, with predicted stabilization energies between 27.0 and 33.4 kcal mol(-1) relative to the reactants, with OH addition to the internal carbon predicted to be 1-4 kcal mol(-1) more stable than addition to the terminal carbon. These stabilization energies result in estimated termolecular rate constants for the OH + MBO reaction using simplified calculations based on RRKM theory that are in reasonable agreement with the experimental values.     

Kinetic studies of the reactions of O2(b 1sigma(g)+) with several atmospheric molecules

Thermal rate coefficients for the removal (reaction + quenching) of O2(1sigma(g)+) by collision with several atmospheric molecules were determined to be as follows: O3, k3(210-370 K) = (3.63 +/- 0.86) x 10(-11) exp((-115 +/- 66)/T); H2O, k4(250-370 K) = (4.52 +/- 2.14) x 10(-12) exp((89 +/- 210)/T); N2, k5(210-370 K) = (2.03 +/- 0.30) x 10(-15) exp((37 +/- 40)/T); CO2, k6(298 K) = (3.39 +/- 0.36) x 10(-13); CH4, k7(298 K) = (1.08 +/- 0.11) x 10(-13); CO, k8(298 K) = (3.74 +/- 0.87) x 10(-15); all units in cm3 molecule(-1) s(-1). O2(1sigma(g)+) was produced by directly exciting ground-state O2(3sigma(g)-) with a 762 nm pulsed dye laser. The reaction of O2(1sigma(g)+) with O3 was used to produce O(3P), and temporal profiles of O(3P) were measured using VUV atomic resonance fluorescence in the presence of the reactant to determine the rate coefficients for removal of O2(1sigma(g)+). Our results are compared with previous values, where available, and the overall trend in the O2(1sigma(g)+) removal rate coefficients and the atmospheric implications of these rate coefficients are discussed. Additionally, an upper limit for the branching ratio of O2(1sigma(g)+) + CO to give O(3P) + CO2 was determined to be < or = 0.2% and this reaction channel is shown to be of negligible importance in the atmosphere.     

Kinetics of the reactions of Cl*(2P(1/2)) and Cl(2P(3/2)) atoms with CH3OH, C2H5OH, n-C3H7OH, and i-C3H7OH at 295 K

The title reactions were studied using laser flash photolysis/laser-induced-fluorescence (FP-LIF) techniques. The two spin-orbit states, Cl*(2P(1/2)) and Cl(2P(3/2)), were detected using LIF at 135.2 and 134.7 nm, respectively. Measured reaction rate constants were as follows (units of cm3 molecule(-1) s(-1)): k(Cl(2P(3/2))+CH3OH) = (5.35 +/- 0.24) x 10(-11), k(Cl(2P(3/2))+C2H5OH) = (9.50 +/- 0.85) x 10(-11), k(Cl(2P(3/2))+n-C3H7OH) = (1.71 +/- 0.11) x 10(-10), and k(Cl(2P(3/2))+i-C3H7OH) = (9.11 +/- 0.60) x 10(-11). Measured rate constants for total removal of Cl*(2P(1/2)) in collisions with CH3OH, C2H5OH, n-C3H7OH, and i-C3H7OH were (1.95 +/- 0.13) x 10(-10), (2.48 +/- 0.18) x 10(-10), (3.13 +/- 0.18) x 10(-10), and (2.84 +/- 0.16) x 10(-10), respectively; quoted errors are two-standard deviations. Although spin-orbit excited Cl*(2P(1/2)) atoms have 2.52 kcal/mol more energy than Cl(2P(3/2)), the rates of chemical reaction of Cl*(2P(1/2)) with CH3OH, C2H5OH, n-C3H7OH, and i-C3H7OH are only 60-90% of the corresponding Cl(2P(3/2)) atom reactions. Under ambient conditions spin-orbit excited Cl* atoms are responsible for 0.5%, 0.5%, 0.4%, and 0.7% of the observed reactivity of thermalized Cl atoms toward CH3OH, C2H5OH, n-C3H7OH, and i-C3H7OH, respectively.     

Determination of the rate constant and product channels for the radical-radical reaction NCO(X 2Pi) + C2H5(X 2A') at 293 K

The rate constant and product branching ratios for the reaction of the cyanato radical, NCO(X (2)Pi), with the ethyl radical, C(2)H(5)(X (2)A'), have been measured over the pressure range of 0.28 to 0.59 kPa and at a temperature of 293 +/- 2 K. The total rate constant, k(1), increased with pressure, P(kPa), described by k(1) = (1.25 +/- 0.16) x 10(-10) + (4.22 +/- 0.35) x 10(-10)P cm(3) molecule(-1) s(-1). Three product channels were observed that were not pressure dependent: (1a) HNCO + C(2)H(4), k(1a) = (1.1 +/- 0.16) x 10(-10), (1b) HONC + C(2)H(4), k(1b) = (2.9 +/- 1.3) x 10(-11), (1c) HCN + C(2)H(4)O, k(1c) = (8.7 +/- 1.5) x 10(-13), with units cm(3) molecule(-1) s(-1) and uncertainties of one-standard deviation in the scatter of the data. The pressure dependence was attributed to a forth channel, (1d), forming recombination products C(2)H(5)NCO and/or C(2)H(5)OCN, with pressure dependence: (1d) k(1d) = (0.090 +/- 1.3) x 10(-11) + (3.91 +/- 0.27) x 10(-10)P cm(3) molecule(-1) s(-1). The radicals were generated by the 248 nm photolysis of ClNCO in an excess of C(2)H(6). Quantitative infrared time-resolved absorption spectrophotometry was used to follow the temporal dependence of the reactants and the appearance of the products. Five species were monitored, HCl, NCO, HCN, HNCO, and C(2)H(4), providing a detailed picture of the chemistry occurring in the system. Other rate constants were also measured: ClNCO + C(2)H(5), k(10) = (2.3 +/- 1.2) x 10(-13) , NCO + C(2)H(6), k(2) = (1.6 +/- 0.11) x 10(-14), NCO + C(4)H(10), k(4) = (5.3 +/- 0.51) x 10(-13), with units cm(3) molecule(-1) s(-1) and uncertainties of one-standard deviation in the scatter of the data.     

Overall rate constant measurements of the reaction of hydroxy- and chloroalkylperoxy radicals derived from methacrolein and methyl vinyl ketone with nitric oxide

The overall rate constants of the reactions of NO with hydroxy- and chloroalkylperoxy radicals, derived from the OH- and Cl-initiated oxidation of methacrolein and methyl vinyl ketone, respectively, were directly determined for the first time using the turbulent-flow technique and pseudo-first-order kinetics conditions with high-pressure chemical ionization mass spectrometry for the direct detection of peroxy radical reactants. The individual 100 Torr, 298 K hydroxyalkylperoxy + NO rate constants for the methacrolein [(0.93 +/- 0.12) (2sigma) x 10(-11) cm3 molecule(-1) s(-1)] and methyl vinyl ketone [(0.84 +/- 0.10) x 10(-11) cm3 molecule(-1) s(-1)] systems were found to be identical within the 95% confidence interval associated with each separate measurement, as were the chloroalkylperoxy + NO rate constants for both methacrolein [(1.17 +/- 0.11) x 10(-11) cm3 molecule(-1) s(-1)] and methyl vinyl ketone [(1.14 +/- 0.14) x 10(-11) cm3 molecule(-1) s(-1)]. However, the difference in the rate constants between the hydroxyperoxy + NO and chloroalkylperoxy + NO systems was found to be statistically significant, with the chloroalkylperoxy + NO rate constants about 30% higher than the corresponding hydroxyalkylperoxy + NO rate constants. This substituent effect was rationalized via a frontier molecular orbital model approach.     

Vibrational energy transfer in O2(X 3sigma(g)-, upsilon=2,3) + O2 collisions at 330 K

Vibrational relaxation of O2(X 3sigma(g)-, upsilon=2,3) by O2 molecules is studied via a two-laser approach. Laser radiation at 266 nm photodissociates ozone in a mixture of molecular oxygen and ozone. The photolysis step produces vibrationally excited O2(a 1delta(g)) that is rapidly converted to O2(X 3sigma(g)-, upsilon=2,3) in a near-resonant adiabatic electronic energy-transfer process involving collisions with ground-state O2. The output of a tunable 193-nm ArF laser monitors the temporal evolution of the O2(X 3sigma(g)-, upsilon=2,3) population via laser-induced fluorescence detected near 360 nm. The rate coefficients for the vibrational relaxation of O2(X 3sigma(g)-, upsilon=2,3) in collision with O2 are 2.0(-0.4)(+0.6) x 10(-13) cm3 s(-1) and (2.6+/-0.4) x 10(-13) cm3 s(-1), respectively. These rate coefficients agree well with other experimental work but are significantly larger than those produced by various semiclassical theoretical calculations.     

Studies of the kinetics and thermochemistry of the forward and reverse reaction Cl + C6H6 = HCl + C6H5

The laser flash photolysis resonance fluorescence technique was used to monitor atomic Cl kinetics. Loss of Cl following photolysis of CCl4 and NaCl was used to determine k(Cl + C6H6) = 6.4 x 10(-12) exp(-18.1 kJ mol(-1)/RT) cm(3) molecule(-1) s(-1) over 578-922 K and k(Cl + C6D6) = 6.2 x 10(-12) exp(-22.8 kJ mol(-1)/RT) cm(3) molecule(-1) s(-1) over 635-922 K. Inclusion of literature data at room temperature leads to a recommendation of k(Cl + C6H6) = 6.1 x 10(-11) exp(-31.6 kJ mol(-1)/RT) cm(3) molecule(-1) s(-1) for 296-922 K. Monitoring growth of Cl during the reaction of phenyl with HCl led to k(C6H5 + HCl) = 1.14 x 10(-12) exp(+5.2 kJ mol(-1)/RT) cm(3) molecule(-1) s(-1) over 294-748 K, k(C6H5 + DCl) = 7.7 x 10(-13) exp(+4.9 kJ mol(-1)/RT) cm(3) molecule(-1) s(-1) over 292-546 K, an approximate k(C6H5 + C6H5I) = 2 x 10(-11) cm(3) molecule(-1) s(-1) over 300-750 K, and an upper limit k(Cl + C6H5I) < or = 5.3 x 10(-12) exp(+2.8 kJ mol(-1)/RT) cm(3) molecule(-1) s(-1) over 300-750 K. Confidence limits are discussed in the text. Third-law analysis of the equilibrium constant yields the bond dissociation enthalpy D(298)(C6H5-H) = 472.1 +/- 2.5 kJ mol(-1) and thus the enthalpy of formation Delta(f)H(298)(C6H5) = 337.0 +/- 2.5 kJ mol(-1).     

A highly sensitive method for time-resolved detection of O(1D) applied to precise determination of absolute O(1D) reaction rate constants and O(3P) yields

We demonstrate detection, in the gas-phase, of O(1D2) at concentrations down to 10(7) cm(-3) and develop this new method for time-resolved kinetic studies allowing both the total removal rate of O(1D2), of up to 1.5 x 10(6) s(-1), and the fraction quenched to O(3P(J)) by species X, k(q)/k(X), to be determined precisely from a single time profile: at 295 K we find, k(O(1D2) + N2O) = (1.43 +/- 0.08) x 10(-10) cm3 s(-1) with k(q)/k(N2O) = 0.056 +/- 0.009; k(O(1D2) + C2H2) = (3.1 +/- 0.2) x 10(-10) cm3 s(-1) with k(q)/k(C2H2) = 0.020 +/- 0.010; k(q)/k(H2O) < 0.003 for O(1D2) + H2O.     

Redox energetics and kinetics of uranyl coordination complexes in aqueous solution

Detailed voltammetric results for five uranyl coordination complexes are presented and analyzed using digital simulations of the voltammetric data to extract thermodynamic (E(1/2)) and heterogeneous electron-transfer kinetic (k(0) and alpha) parameters for the one-electron reduction of UO(2)(2+) to UO(2)(+). The complexes and their corresponding electrochemical parameters are the following: [UO(2)(OH(2))(5)](2+) (E(1/2) = -0.169 V vs Ag/AgCl, k(0) = 9.0 x 10(-3) cm/s, and alpha = 0.50); [UO(2)(OH)(5)](3-) (-0.927 V, 2.8 x 10(-3) cm/s, 0.46); [UO(2)(C(2)H(3)O(2))(3)](-) (-0.396 V, approximately 0.1 cm/s, approximately 0.5); [UO(2)(CO(3))(3)](4-) (-0.820 V, 2.6 x 10(-5) cm/s, 0.41); [UO(2)Cl(4)](2-) (-0.065 V, 9.2 x 10(-3) cm/s, 0.30). Differences in the E(1/2) values are attributable principally to differences in the basicity of the equatorial ligands. Differences in rate constants are considered within the context of Marcus theory of electron transfer, but no specific structural change(s) in the complexes between the two oxidation states can be uniquely identified with the underlying variability in the heterogeneous rate constants and electron-transfer coefficients.     

A gas-phase kinetic study of the reaction between bromine monoxide and methylperoxy radicals at atmospheric temperatures

The rate constant of the reaction of BrO with CH(3)O(2) was determined to be k1 = (6.2 +/- 2.5) x 10(-12) cm3 molecule(-1) s(-1) at 298 K and 100-200 Torr of O2 diluent. Quoted uncertainty was two standard deviations. No significant pressure dependence of the rate constants was observed at 100-200 Torr total pressure of N2 or O2 diluents. Temperature dependence of the rate constants was further investigated over the range 233-333 K, and an Arrhenius type expression was obtained for k1 = 4.6 x 10(-13) exp[(798 +/- 76)/T] cm3 molecule(-1) s(-1). The product branching ratios were evaluated and the atmospheric implications were discussed.     

The dissociation constants of alizarin fluorine blue

Dissociation constants for the analytical reagent alizarin fluorine blue (3-aminomethylalizarin-N N-diacetic acid) have been determined by potentiometric titration at ionic strength 0.1, and are k(1) = 1.28 +/- 0.30 x 10(-5); k(2) = 2.82 +/- 0.24 x 10(-8); k(3) = 3.72 +/- 0.19 x 10(-11); k(4) = 6.39 +/- 0.12 x 10(-12).     

Kinetics studies of aqueous phase reactions of Cl atoms and Cl2(-) radicals with organic sulfur compounds of atmospheric interest

A laser flash photolysis-long path UV-visible absorption technique has been employed to investigate the kinetics of aqueous phase reactions of chlorine atoms (Cl) and dichloride radicals (Cl2(-)) with four organic sulfur compounds of atmospheric interest, dimethyl sulfoxide (DMSO; CH3S(O)CH3), dimethyl sulfone (DMSO2; CH3(O)S(O)CH3), methanesulfinate (MSI; CH3S(O)O-), and methanesulfonate (MS; CH3(O)S(O)O-). Measured rate coefficients at T = 295 +/- 1 K (in units of M(-1) s(-1)) are as follows: Cl + DMSO, (6.3 +/- 0.6) x 10(9); Cl2(-) + DMSO, (1.6 +/- 0.8) x 10(7); Cl + DMSO2, (8.2 +/- 1.6) x 10(5); Cl2(-) + DMSO2, (8.2 +/- 5.5) x 10(3); Cl2(-) + MSI, (8.0 +/- 1.0) x 10(8); Cl + MS, (4.9 +/- 0.6) x 10(5); Cl2(-) + MS, (3.9 +/- 0.7) x 10(3). Reported uncertainties are estimates of accuracy at the 95% confidence level and the rate coefficients for MSI and MS reactions with Cl2(-) are corrected to the zero ionic strength limit. The absorption spectrum of the DMSO-Cl adduct is reported; peak absorbance is observed at 390 nm and the peak extinction coefficient is found to be 5760 M(-1) cm(-1) with a 2sigma uncertainty of +/-30%. Some implications of the new kinetics results for understanding the atmospheric sulfur cycle are discussed.