P. H. Wine

Auburn University, Auburn, Alabama, United States

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Publications (148)283.38 Total impact

  • E. G. Estupinan · J. M. Nicovich · P. H. Wine
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    ABSTRACT: ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.
    No preview · Article · Dec 2010 · ChemInform
  • Michael L. McKee · P. H. Wine
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    ABSTRACT: ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.
    No preview · Article · May 2010 · ChemInform
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    ABSTRACT: A laser flash photolysis-resonance fluorescence technique has been employed to measure rate coefficients and physical vs. reactive quenching branching ratios for O((1)D) deactivation by three potent greenhouse gases, SO(2)F(2)(k(1)), NF(3)(k(2)), and SF(5)CF(3)(k(3)). In excellent agreement with one published study, we find that k(1)(T) = 9.0 x 10(-11) exp(+98/T) cm(3) molecule(-1) s(-1) and that the reactive quenching rate coefficient is k(1b) = (5.8 +/- 2.3) x 10(-11) cm(3) molecule(-1) s(-1) independent of temperature. We find that k(2)(T) = 2.0 x 10(-11) exp(+52/T) cm(3) molecule(-1) s(-1) with reaction proceeding almost entirely (approximately 99%) by reactive quenching. Reactive quenching of O((1)D) by NF(3) is more than a factor of two faster than reported in one published study, a result that will significantly lower the model-derived atmospheric lifetime and global warming potential of NF(3). Deactivation of O((1)D) by SF(5)CF(3) is slow enough (k(3) < 2.0 x 10(-13) cm(3) molecule(-1) s(-1) at 298 K) that reaction with O((1)D) is unimportant as an atmospheric removal mechanism for SF(5)CF(3). The kinetics of O((1)D) reactions with SO(2) (k(4)) and CS(2) (k(5)) have also been investigated at 298 K. We find that k(4) = (2.2 +/- 0.3) x 10(-10) and k(5) = (4.6 +/- 0.6) x 10(-10) cm(3) molecule(-1) s(-1); branching ratios for reactive quenching are 0.76 +/- 0.12 and 0.94 +/- 0.06 for the SO(2) and CS(2) reactions, respectively. All uncertainties reported above are estimates of accuracy (2sigma) and rate coefficients k(i)(T) (i = 1,2) calculated from the above Arrhenius expressions have estimated accuracies of +/- 15% (2sigma).
    Full-text · Article · Apr 2010 · Proceedings of the National Academy of Sciences
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    ABSTRACT: The kinetics of the reactions CH3 + HBr, CD3 + HBr, CH3 + DBr, C2H5 + HBr, C2H5 + DBr, t-C4H9 + HBr, and t-C4H9 + DBr is studied as a function of temperature (257-430 K) and pressure (10-300 Torr of N2). Time-resolved resonance fluorescence detection of Br atom appearance following laser flash photolysis of RI was used in the experiments. Results show that the rates of all reactions increased as the temperature decreased.
    No preview · Article · Mar 2010 · ChemInform
  • P. H. Wine · P. L. Laine · Z. Zhao · J. M. Nicovich
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    ABSTRACT: Dimethylsulfide (DMS) is emitted into the atmosphere in large quantities from the oceans, and its oxidation products are thought to play an important role in particle formation and growth in marine environments. It has been suggested that DMS cycling through the ocean-atmosphere system influences global climate [Charlson et al, Nature, 1987, 326, 655-661]. The atmospheric oxidation of DMS can be initiated by a number of radicals including OH, NO3, halogen atoms, and halogen monoxides. Quantitative assessment of the role of the Cl atom as a DMS oxidant in the marine boundary layer is currently not possible because (i) Cl mixing ratios are not well established and (ii) there is considerable uncertainty in both the rate and the mechanism of the Cl + DMS reaction. We report new experiments that address the kinetics of three important elementary steps in the Cl + DMS reaction mechanism. Temperature dependent rate constants have been measured in 1 Torr of He bath gas, i.e., under conditions where addition of Cl to the sulfur atom is very slow and overall reactivity is dominated by the H-abstraction reaction. We find that kabs = 7.0 x 10-11 exp(+340/T) cm3 molecule-1 s-1, a result that agrees well with the low pressure results of Stickel et al. [J. Phys. Chem., 1992, 96, 9875-9883], but disagrees significantly with the results of Diaz-de-Mera et al. [J. Phys. Chem. A, 2002, 106, 8627-8633]. Pressure-dependent rate constant measurements at atmospheric temperatures establish overall rate constants which, after subtraction of kabs(T), yield rate constants for adduct formation, kadd(P,T). At temperatures around 420 K and high pressures (around 500 Torr N2), kinetic evidence for reversible adduct formation is observed. Adduct structural information obtained from quantum chemical calculations is used to evaluate DeltaS(T) and DeltaCp(T), which are employed in conjunction with the measured equilibrium constant for adduct formation/dissociation to evaluate DeltaH(T). At 298 K, the adduct bond dissociation enthalpy is 95 ± 8 kJ/mol which is near the high end of a rather wide range of theoretical values reported in the literature. The above information facilitates the determination of equilibrium constants for adduct formation/dissociation at atmospheric temperatures which, in conjunction with kadd(P,T) values determined as described above, allow temperature-dependent rate constants for adduct dissociation to be evaluated. At a pressure of 1 atm, the DMS-Cl lifetime toward dissociation to Cl + DMS increases with decreasing temperature from a few seconds at 300 K to many hours at 250 K; these lifetimes are sufficiently long that atmospheric DMS-Cl destruction pathways other than unimolecular decomposition are likely to be important.
    No preview · Article · Dec 2009
  • P. L. Laine · J. M. Nicovich · P. H. Wine
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    ABSTRACT: Halogenated alkanes are present in our atmosphere as a result of both natural and anthropogenic sources. The bromoalkanes ethyl bromide (CH3CH2Br), n-propylbromide (CH3CH2CH2Br), and 1,2-dibromoethane (CH2BrCH2Br) are emitted into the atmosphere from anthropogenic sources, and are thought to play a role in stratospheric ozone depletion. While the primary tropospheric sink for the above bromocarbons is reaction with OH radicals, reaction with chlorine atoms may also represent a non-negligible sink. We have coupled production of Cl by laser flash photolysis with time-resolved monitoring of Br atom appearance by atomic resonance fluorescence spectroscopy to study the kinetics of the title reactions over a wide range of temperature and pressure. Atomic Br is generated by rapid dissociation of the CH2CH2Br product of Cl + CH3CH2Br, the CH3CHCH2Br product of Cl + CH3CH2CH2Br, and the only possible H-abstraction product of Cl + CH2BrCH2Br. By comparing product Br signal strengths with those obtained when Cl removal is dominated by reaction with Br2, temperature-dependent branching ratios for abstraction of the â hydrogen are obtained for the Cl + CH3CH2Br and Cl + CH3CH2CH2Br reactions.
    No preview · Article · Dec 2008
  • Z. Zhao · J. M. Nicovich · M. L. McKee · P. H. Wine
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    ABSTRACT: Numerous theoretical and experimental studies have suggested that HO2 radicals are able to form strong hydrogen bonds with some closed-shell species, which can potentially influence our understanding of HO2 chemistry in the upper troposphere and lower stratosphere. In this study, a laser flash photolysis-tunable diode laser absorption spectroscopy technique has been employed to study the formation of HO2 complexes with formic and acetic acids. At low temperatures, equilibration kinetics have been observed, allowing adduct formation and dissociation rate coefficients to be obtained and adduct binding enthalpies to be determined. This is the first experimental study of the HO2-carboxylic acid complexes and the binding energies are in good agreement with the most recent theoretical estimates. The potential role of HO2-RC(O)OH adducts in atmospheric chemistry will be discussed.
    No preview · Article · Dec 2008
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    ABSTRACT: Time-resolved UV-visible absorption spectroscopy has been coupled with UV laser flash photolysis of Cl2/RI/N2/X mixtures (R = CH3 or C2H5; X = O2, NO, or NO2) to generate the RI-Cl radical adducts in the gas phase and study the spectroscopy and reaction kinetics of these species. Both adducts were found to absorb strongly over the wavelength range 310-500 nm. The spectra were very similar in wavelength dependence with lambda(max) approximately 315 nm for both adducts and sigma(max) = (3.5 +/- 1.2) x 10(-17) and (2.7 +/- 1.0) x 10(-17) cm(2) molecule(-1) (base e) for CH3I-Cl and C2H5I-Cl, respectively (uncertainties are estimates of accuracy at the 95% confidence level). Two weaker bands with lambda max approximately 350 and 420 nm were also observed. Over the wavelength range 405-500 nm, where adduct spectra are reported both in the literature and in this study, the absorption cross sections obtained in this study are a factor of approximately 4 lower than those reported previously [Enami et al. J. Phys. Chem. A 2005, 109, 1587 and 6066]. Reactions of RI-Cl with O2 were not observed, and our data suggest that upper limit rate coefficients for these reactions at 250 K are 1.0 x 10(-17) cm(3) molecule(-1) s(-1) for R = CH3 and 2.5 x 10(-17) cm(3) molecule(-1) s(-1) for R = C2H5. Their lack of reactivity with O2 suggests that RI-Cl adducts are unlikely to play a significant role in atmospheric chemistry. Possible reactions of RI-Cl with RI could not be confirmed or ruled out, although our data suggest that upper limit rate coefficients for these reactions at 250 K are 3 x 10(-13) cm(3) molecule(-1) s(-1) for R = CH3 and 5 x 10(-13) cm(3) molecule(-1) s(-1) for R = C2H5. Rate coefficients for CH3I-Cl reactions with CH3I-Cl (k9), NO (k22), and NO2 (k24), and C2H5I-Cl reactions with C2H5I-Cl (k14), NO (k23), and NO2 (k25) were measured at 250 K. In units of 10(-11) cm(3) molecule(-1) s(-1), the rate coefficients were found to be 2k9 = 35 +/- 12, k22 = 1.8 +/- 0.4, k24 = 3.3 +/- 0.6, 2k14 = 40 +/- 16, k23 = 1.8 +/- 0.3, and k25 = 4.0 +/- 0.9, where the uncertainties are estimates of accuracy at the 95% confidence level.
    No preview · Article · Jul 2008 · The Journal of Physical Chemistry A
  • Z. Zhao · D. T. Huskey · J. M. Nicovich · P. H. Wine
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    ABSTRACT: A laser flash photolysis–resonance fluorescence technique has been employed to study the kinetics of the reactions of atomic chlorine with acetone (CH3C(O)CH3; k1), 2-butanone (C2H5C(O)CH3; k2), and 3-pentanone (C2H5C(O)C2H5; k3) as a function of temperature (210–440 K) and pressure (30–300 Torr N2). No significant pressure dependence is observed for any of the reactions studied. Arrhenius expressions (units are 10−11 cm3 molecule−1 s−1) obtained from the data are k1(T) = (1.53 ± 0.19) exp[(−594 ± 33)/T], k2(T) = (2.77 ± 0.33) exp[(+76 ± 33)/T], and k3(T) = (5.66 ± 0.41) exp[(+87 ± 22)/T], where uncertainties are 2σ and represent precision only. The accuracy of reported rate coefficients is estimated to be ±15% over the entire range of pressure and temperature investigated. The room temperature rate coefficients reported in this study are in good agreement with a majority of literature values. However, the activation energies reported in this study are in poor agreement with the literature values, particularly for 2-butanone and 3-pentanone. Possible explanations for discrepancies in published kinetic parameters are proposed, and the potential role of Cl + ketone reactions in atmospheric chemistry is discussed. © 2008 Wiley Periodicals, Inc. Int J Chem Kinet 40: 259–267, 2008
    No preview · Article · May 2008 · International Journal of Chemical Kinetics
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    ABSTRACT: Iodinated hydrocarbons are emitted from natural, mostly oceanic, sources. The high fluxes of these species (dominated by methyl iodide, but including larger species as well) and their short photochemical lifetime imply potentially significant impacts on the chemistry of the marine boundary layer. Recently, we have employed a variety of experimental and theoretical methods to study the oxidation of organic iodides under atmospheric conditions. Compounds studied include a model compound, CF3CH2I, as well as ethyl and propyl iodides. While our studies have generally involved Cl-atom initiated processes, many of the results can be generalized to OH-initiated attack. General concepts to be discussed, in the context of the atmospheric behavior of these species, include: 1) The rates of destruction of iodinated organics via reaction with Cl-atom, and a comparison with other loss processes; 2) Oxidation pathways and end-product distributions, with a focus on the formation of alkenes from decomposition of beta-iodoalkyl radicals; and the mechanism of the reaction of alpha-iodoalkyl radicals with molecular oxygen; and 3) The reversible formation of Cl / iodoalkane adducts, and the subsequent chemistry of these species.
    No preview · Article · Dec 2007
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    ABSTRACT: A laser flash photolysis-resonance fluorescence technique has been employed to study the kinetics of the reaction of atomic chlorine with pyridine (C(5)H(5)N) as a function of temperature (215-435 K) and pressure (25-250 Torr) in nitrogen bath gas. At T> or = 299 K, measured rate coefficients are pressure independent and a significant H/D kinetic isotope effect is observed, suggesting that hydrogen abstraction is the dominant reaction pathway. The following Arrhenius expression adequately describes all kinetic data at 299-435 K for C(5)H(5)N: k(1a) = (2.08 +/- 0.47) x 10(-11) exp[-(1410 +/- 80)/T] cm(3) molecule(-1) s(-1) (uncertainties are 2sigma, precision only). At 216 K < or =T< or = 270 K, measured rate coefficients are pressure dependent and are much faster than computed from the above Arrhenius expression for the H-abstraction pathway, suggesting that the dominant reaction pathway at low temperature is formation of a stable adduct. Over the ranges of temperature, pressure, and pyridine concentration investigated, the adduct undergoes dissociation on the time scale of our experiments (10(-5)-10(-2) s) and establishes an equilibrium with Cl and pyridine. Equilibrium constants for adduct formation and dissociation are determined from the forward and reverse rate coefficients. Second- and third-law analyses of the equilibrium data lead to the following thermochemical parameters for the addition reaction: Delta(r)H = -47.2 +/- 2.8 kJ mol(-1), Delta(r)H = -46.7 +/- 3.2 kJ mol(-1), and Delta(r)S = -98.7 +/- 6.5 J mol(-1) K(-1). The enthalpy changes derived from our data are in good agreement with ab initio calculations reported in the literature (which suggest that the adduct structure is planar and involves formation of an N-Cl sigma-bond). In conjunction with the well-known heats of formation of atomic chlorine and pyridine, the above Delta(r)H values lead to the following heats of formation for C(5)H(5)N-Cl at 298 K and 0 K: Delta(f)H = 216.0 +/- 4.1 kJ mol(-1), Delta(f)H = 233.4 +/- 4.6 kJ mol(-1). Addition of Cl to pyridine could be an important atmospheric loss process for pyridine if the C(5)H(5)N-Cl product is chemically degraded by processes that do not regenerate pyridine with high yield.
    No preview · Article · Aug 2007 · Physical Chemistry Chemical Physics
  • K.M. Kleissas · J.M. Nicovich · P.H. Wine
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    ABSTRACT: Time-resolved UV–vis absorption spectroscopy has been coupled with 248nm laser flash photolysis of Cl2CO in the presence of CH3S(O)CH3 (and in some cases O2, NO, or NO2) to generate the CH3(Cl)S(O)CH3 radical adduct in the gas phase and study the spectroscopy and kinetics of this species at 296K. CH3(Cl)S(O)CH3 is found to possess a strong absorption band with λmax=394nm and σmax=(4.0±1.4)×10−17cm2molecule−1 (base e); the gas phase spectrum of CH3(Cl)S(O)CH3 is very similar to previously reported liquid phase spectra in chloroalkane and water solvents. Reaction of CH3(Cl)S(O)CH3 with O2 is found to be very slow, and our data suggest that the rate coefficient for this reaction is less than 3×10−18cm3molecule−1s−1. Rate coefficients for CH3(Cl)S(O)CH3 reactions with CH3(Cl)S(O)CH3 (k3), NO (k9), and NO2 (k10) in units of 10−11cm3molecule−1s−1 are found to be 2k3=6.0±2.4, k9=1.2±0.3, and k10=2.1±0.3, where the uncertainties are estimates of accuracy at the 95% confidence level.
    No preview · Article · Mar 2007 · Journal of Photochemistry and Photobiology A Chemistry
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    ABSTRACT: A laser flash photolysis-resonance fluorescence technique has been employed to study the kinetics of the reaction of chlorine atoms with dimethyl sulfoxide (CH3S(O)CH3; DMSO) as a function of temperature (270-571 K) and pressure (5-500 Torr) in nitrogen bath gas. At T = 296 K and P > or = 5 Torr, measured rate coefficients increase with increasing pressure. Combining our data with literature values for low-pressure rate coefficients (0.5-3 Torr He) leads to a rate coefficient for the pressure independent H-transfer channel of k1a = 1.45 x 10(-11) cm3 molecule(-1) s(-1) and the following falloff parameters for the pressure-dependent addition channel in N2 bath gas: k(1b,0) = 2.53 x 10(-28) cm6 molecule(-2) s(-1); k(1b,infinity) = 1.17 x 10(-10) cm3 molecule(-1) s(-1), F(c) = 0.503. At the 95% confidence level, both k1a and k1b(P) have estimated accuracies of +/-30%. At T > 430 K, where adduct decomposition is fast enough that only the H-transfer pathway is important, measured rate coefficients are independent of pressure (30-100 Torr N2) and increase with increasing temperature. The following Arrhenius expression adequately describes the temperature dependence of the rate coefficients measured at over the range 438-571 K: k1a = (4.6 +/- 0.4) x 10(-11) exp[-(472 +/- 40)/T) cm3 molecule(-1) s(-1) (uncertainties are 2sigma, precision only). When our data at T > 430 K are combined with values for k1a at temperatures of 273-335 K that are obtained by correcting reported low-pressure rate coefficients from discharge flow studies to remove the contribution from the pressure-dependent channel, the following modified Arrhenius expression best describes the derived temperature dependence: k1a = 1.34 x 10(-15)T(1.40) exp(+383/T) cm3 molecule(-1) s(-1) (273 K < or = T < or = 571 K). At temperatures around 330 K, reversible addition is observed, thus allowing equilibrium constants for Cl-DMSO formation and dissociation to be determined. A third-law analysis of the equilibrium data using structural information obtained from electronic structure calculations leads to the following thermochemical parameters for the association reaction: delta(r)H(o)298 = -72.8 +/- 2.9 kJ mol(-1), deltaH(o)0 = -71.5 +/- 3.3 kJ mol(-1), and delta(r)S(o)298 = -110.6 +/- 4.0 J K(-1) mol(-1). In conjunction with standard enthalpies of formation of Cl and DMSO taken from the literature, the above values for delta(r)H(o) lead to the following values for the standard enthalpy of formation of Cl-DMSO: delta(f)H(o)298 = -102.7 +/- 4.9 kJ mol(-1) and delta(r)H(o)0 = -84.4 +/- 5.8 kJ mol(-1). Uncertainties in the above thermochemical parameters represent estimated accuracy at the 95% confidence level. In agreement with one published theoretical study, electronic structure calculations using density functional theory and G3B3 theory reproduce the experimental adduct bond strength quite well.
    No preview · Article · Jun 2006 · The Journal of Physical Chemistry A
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    ABSTRACT: HCN profiles measured by solar occultation spectrometry during 10 balloon flights of the JPL MkIV instrument are presented. The HCN profiles reveal a compact correlation with stratospheric tracers. Calculations with a 2D-model using established rate coefficients for the reactions of HCN with OH and O(D-1) severely underestimate the measured HCN in the middle and upper stratosphere. The use of newly available rate coefficients for these reactions gives reasonable agreement of measured and modeled HCN. An HCN yield of similar to 30% from the reaction of CH3CN with OH is consistent with the measurements.
    No preview · Article · Jan 2006 · Geophysical Research Letters
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    ABSTRACT: Time-resolved UV–vis absorption spectroscopy (TRUVVAS) has been coupled with 248nm laser flash photolysis (LFP) of Cl2CO in the presence of CS2 (and in some cases O2, NO or NO2) to generate the CS2Cl radical adduct in the gas phase and study the spectroscopy and kinetics of this species. CS2Cl is found to possess a strong absorption band at λmax≈365nm with σmax=(2.3±0.7)×10−17cm2molecule−1 (base e) and a weaker band at λmax≈480nm; the gas-phase spectrum of CS2Cl is very similar to the previously reported liquid-phase spectrum in CCl4 solvent. Reaction of CS2Cl with O2 is found to be very slow; our data suggest that the rate coefficient for this reaction at 240K is less than 5.0×10−18cm3molecule−1s−1. Rate coefficients for CS2Cl reactions with CS2Cl (k3), NO (k5), and NO2 (k6) were measured at 240K and, in units of 10−11cm3molecule−1s−1, were found to be 2k3=15±6, k5=2.2±0.5, and k6=1.3±0.4, where the uncertainties are estimates of accuracy at the 95% confidence level.
    No preview · Article · Dec 2005 · Journal of Photochemistry and Photobiology A Chemistry
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    ABSTRACT: A pulsed laser photolysis–resonance fluorescence technique was employed independently by two laboratories to measure ΦO3P, the quantum yield for production of O(3P) from O3 photolysis at 248 nm, between 196 and 427 K. The agreement between the two studies is very good, and the combined results are adequately represented by the function ΦO3P= (0.115 ± 0.030) × exp((35 ± 60)/T) where the uncertainties are 2σ. Within experimental uncertainties, the new results are in agreement with previously reported room temperature results as well as with the single previous temperature dependence study, and greatly reduce the uncertainties in ΦO3P(T) and ΦO1D(T) (=1− ΦO3P(T)) especially at temperatures other than room temperature. The yield of O(3P) in the reaction of O(1D) with O3 is shown to be greater than unity at room temperature and below, and to increase slightly with decreasing temperature.
    Full-text · Article · Dec 2004 · Physical Chemistry Chemical Physics
  • R. S. Strekowski · J. M. Nicovich · P. H. Wine
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    ABSTRACT: A laser flash photolysis–resonance fluorescence technique has been employed to investigate the kinetics of the reactions of electronically excited oxygen atoms, O(1D2), with N2 (k1) and O2 (k2) as a function of temperature (197–427 K) in helium buffer gas at pressures of 11–40 Torr. The results are well-described by the following Arrhenius expressions (units are 10−11 cm3 molecule−1 s−1): k1(T)=(1.99±0.06) exp{(145±9)/T} and k2(T)=(3.39±0.03) exp{(63±3)/T}. Uncertainties in the Arrhenius parameters are 2σ and represent precision only; estimated accuracies of reported k1(T) and k2(T) values at the 95% confidence level are ±10% around room temperature and ±15% at the temperature extremes of the study. The O(1D2)+O2 kinetic data reported in this study are in very good agreement with available literature values. However, the kinetic data reported in this study (and two other new studies reported in this issue) suggest that the O(1D2)+N2 reaction is significantly faster than previously thought, a finding that has important implications regarding production rates of tropospheric HOx radicals as well as stratospheric HOx and NOx radicals calculated in atmospheric models.
    No preview · Article · May 2004 · Physical Chemistry Chemical Physics
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    Lei Zhu · J. M Nicovich · P. H Wine
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    ABSTRACT: A laser flash photolysis-long path UV-Vis absorption technique has been employed to investigate the aqueous phase reactions between the SO4- radical and three organic sulfur species of atmospheric interest, dimethylsulfoxide (DMSO; CH3S(O)CH3), dimethylsulfone (DMSO2; CH3(O)S(O)CH3), and methanesulfonate (MS; CH3(O)S(O)O-). Rate coefficients at T=298 K in units of M-1 s(-1) are found to be (3.0+/-0.4)x10(9) for DMSO, <(3.9&PLUSMN;0.5)x10(6) for DMSO2, and (1.1&PLUSMN;0.3)x10(4) for MS (zero ionic strength limit); reported uncertainties are estimates of accuracy at the 95% confidence level. Temperature-dependent studies have been carried out over the range 278-311 K; activation energies in units of kJ mol(-1) are found to be 12.0&PLUSMN;0.4 for DMSO, 11.3&PLUSMN;1.3 for DMSO2 and 20.7&PLUSMN;4.3 for MS (zero ionic strength limit), where uncertainties are 2σ and represent precision only. Accuracies of rate coefficients measured at the temperature extremes of our study are thought to be similar to those reported above for the 298 K rate coefficients. The implications of the kinetics results for understanding the atmospheric sulfur cycle are discussed.
    Full-text · Article · May 2003 · Journal of Photochemistry and Photobiology A Chemistry
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    ABSTRACT: Tunable diode laser absorption spectroscopy has been employed to measure the amount of N2O produced from laser flash photolysis of O3/N2/O2 mixtures at 266 and 532 nm. In the 532 nm photolysis experiments very little N2O is observed, thus allowing an upper limit yield of 7 x 10(exp -8) to be established for the process O3 + N2 yield N2O + O2, where O3 is nascent O3 that is newly formed via O(3P(sub J)) + O2 recombination (with vibrational excitation near the dissociation energy of O3). The measured upper limit yield is a factor of approx. 600 smaller than a previous literature value and is approximately a factor of 10 below the threshold for atmospheric importance. In the 266 nm photolysis experiments, significant N2O production is observed and the N2O quantum yield is found to increase linearly with pressure over the range 100 - 900 Torr in air bath gas. The source of N2O in the 266 nm photolysis experiments is believed to be the addition reaction O(1D(sub 2)) + N2 + M yields (k(sub sigma)) N2O + M, although reaction of (very short-lived) electronically excited O3 with N2 cannot be ruled out by the available data. Assuming that all observed N2O comes from the O(1D(sub 2)) + N2 + M reaction, the following expression describes the temperature dependence of k(sub sigma) (in its third-order low-pressure limit) that is consistent with the N2O yield data: k(sub sigma) = (2.8 +/- 0.1) x 10(exp -36)(T/300)(sup -(0-88+0.36)) cm(sup 6) molecule(sup -2)/s, where the uncertainties are 2(sigma) and represent precision only. The accuracy of the reported rate coefficients at the 95% confidence level is estimated to be 30 - 40% depending on the temperature. Model calculations suggest that gas phase processes initiated by ozone absorption of a UV photon represent about 1.4% of the currently estimated global source strength of atmospheric N2O. However, these processes could account for a significant fraction of the oxygen mass-independent enrichment observed in atmospheric N2O, and they appear to be the first suggested photochemical mechanism that is capable of explaining the altitude dependence of the observed mass -independent isotopic signature.
    Full-text · Article · Nov 2002
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    ABSTRACT: The rate coefficient for the reaction of O(1D) with N2 at 295 K has been measured in three laboratories to be 3.1 × 10-11 cm3 molecule-1 s-1, with an uncertainty of 10% at the 95% confidence level, and to be 2.1 × 10-11 exp {(115 +/- 10) /T} cm3 molecule-1 s-1 as a function of temperature. (The quoted uncertainty in E/R will allow calculation of the uncertainty in the rate constant at various temperatures.) The implications of this finding are to decrease the calculated OH production rate via the reaction of O(1D) with H2O in the atmosphere by roughly 15% in the mid-troposphere and above and to greatly reduce the uncertainties in the calculated HOx and NOx production rates in the atmosphere.
    Full-text · Article · Aug 2002 · Geophysical Research Letters

Publication Stats

3k Citations
283.38 Total Impact Points

Institutions

  • 1996-2010
    • Auburn University
      • Department of Chemistry & Biochemistry
      Auburn, Alabama, United States
  • 1979-2010
    • Georgia Institute of Technology
      • • School of Chemistry and Biochemistry
      • • School of Earth and Atmospheric Sciences
      Atlanta, Georgia, United States
  • 1985-1995
    • Georgia Tech Research Institute
      Atlanta, Georgia, United States
  • 1981
    • Livermore Instruments
      Oakland, California, United States