Dieter Bauer

University of Miami, Coral Gables, FL, United States

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Publications (9)23.67 Total impact

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    ABSTRACT: A pulsed laser photolysis-pulsed laser induced fluorescence technique has been employed to study the recombination of mercury and bromine atoms, Hg + Br + M --> HgBr + M (1) and the self-reaction of bromine atoms, Br + Br + M --> Br2 + M (2). Rate coefficients were determined as a function of pressure (200-600 Torr) and temperature (243-293 K) in nitrogen buffer gas and as a function of pressure (200-600 Torr) in helium buffer gas at room temperature. For reaction 1, kinetic measurements were performed under conditions in which bromine atoms were the reactant in excess concentration while simultaneously monitoring the concentration of both mercury and bromine. A temperature dependent expression of (1.46 +/- 0.34) x 10(-32) x (T/298)(-(1.86+/-1.49)) cm6 molecule(-2) s(-1) was determined for the third-order recombination rate coefficient in nitrogen buffer gas. The effective second-order rate coefficient for reaction 1 under atmospheric conditions is a factor of 9 smaller than previously determined in a recently published relative rate study. For reaction 2 we obtain a temperature dependent expression of (4.31 +/- 0.21) x 10(-33) x (T/298)(-(2.77+/-0.30)) cm6 molecule(-2) s(-1) for the third-order recombination rate coefficient in nitrogen buffer gas. The rate coefficients are reported with a 2sigma error of precision only; however, due to the uncertainty in the determination of absolute bromine atom concentrations and other unidentified systematic errors we conservatively estimate an uncertainty of +/-50% in the rate coefficients. For both reactions the observed pressure, temperature and buffer gas dependencies are consistent with the expected behavior for three-body recombination.
    The Journal of Physical Chemistry A 06/2006; 110(21):6623-32. · 2.77 Impact Factor
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    ABSTRACT: A pulsed laser photolysis-pulsed laser induced fluorescence technique has been employed to study the recombination of mercury and chlorine atoms, Hg + Cl + M --> HgCl + M (1), and the self-reaction of chlorine atoms, Cl + Cl + M --> Cl(2) + M (2). Rate coefficients were determined as a function of pressure (200-600 Torr) and temperature (243-293 K) in N(2) buffer gas and as a function of pressure (200-600 Torr) in He buffer gas at room temperature. For reaction (1) kinetic measurements were obtained under conditions in which either mercury or chlorine atoms were the reactant in excess concentration while simultaneously monitoring the concentration of both reactants. An Arrhenius expression of (2.2 +/- 0.5) x 10(-32) exp{(680 +/- 400)((1)/(T) - (1)/(298))} cm(6) molecule(-2) s(-1) was determined for the third-order recombination rate coefficient in nitrogen buffer gas. The effective second-order rate coefficient for reaction 1 under atmospheric conditions is much smaller than prior determinations using relative rate techniques. For reaction (2) we obtain an Arrhenius expression of (8.4 +/- 2.3) x 10(-33) exp{(850 +/- 470)((1)/(T) - (1)/(298))} cm(6) molecule(-2) s(-1) for the third-order recombination rate coefficient in nitrogen buffer gas. The rate coefficients are reported with a 2sigma error of precision only; however, due to the uncertainty in the determination of absolute chlorine atom concentrations we conservatively estimate an uncertainty of +/-50% in the rate coefficients. For both reactions the observed pressure, temperature, and buffer gas dependencies are consistent with the expected behavior for three-body recombination.
    The Journal of Physical Chemistry A 09/2005; 109(34):7732-41. · 2.77 Impact Factor
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    ABSTRACT: The kinetics and mechanism of the three-body recombination of OH with NO2 were studied using a pulsed laser photolysis pulsed laser induced fluorescence technique. The rate coefficients for deactivation of vibrationally excited OH (v = 1-5) by NO2 were found to be independent of vibrational level with a value of (6.4 +/- 0.3) x 10(-11) cm3 molecule s (-1) at 298 K. The rate coefficient for reaction of 18OH with NO2 was measured and found to be much faster than for unlabeled OH with a "zero pressure" rate of 1 x 10(-11) cm3 molecule(-1) s(-1) at 298 K and 273 K. Observation of temporal profiles of 16OH and 18OH suggest that isotopic scrambling in the initially formed [H18ON16O2] complex is complete on the microsecond time scale of our experiments. The rate coefficient for reaction of unlabeled OH with NO2 was measured at 413 K in 400 Torr of He. Biexponential temporal profiles were obtained and are consistent with a 10 +/- 3% yield of the weakly bound HOONO isomer.
    Faraday Discussions 02/2005; 130:111-23; discussion 125-51, 519-24. · 3.82 Impact Factor
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    ABSTRACT: The deactivation kinetics of vibrationally excited OH X 2Π (v = 1–5) were studied using a pulsed laser photolysis-pulsed laser induced fluorescence technique. Temporal profiles of OH (v) were obtained by exciting off-diagonal (Δv = −1,−3) transitions in the A–X band of OH and monitoring the diagonal, blue shifted fluorescence. Photolysis of O3 at 266 nm was used to produce O1D which reacted rapidly with H2, CH4 and H2O to produce OH (v). Deactivation rate coefficients for OH (v = 1–5) with O2 and N2 and for OH (v = 2,1) with O3 were obtained. The deactivation rate coefficients show an exponential dependence on vibrational level for both O2 and N2, however O2 is much more efficient.
    Physical Chemistry Chemical Physics 01/2004; 6(17). · 3.83 Impact Factor
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    ABSTRACT: We have examined the sensitivity of single and sequential two-photon laser-induced fluorescence (LIF) techniques for the detection of elemental mercury, Hg(0), in the gas phase. Single photon LIF involves excitation of the 63P1–61S0 transition at 253.7nm, followed by observation of resonance fluorescence. Sequential two-photon techniques follow the initial 63P1–61S0 excitation with a second excitation step to either the 71S0 or 73S1 levels followed by observation of blue or red shifted fluorescence. We have examined four variants of these approaches which all exceed the sensitivity of single photon LIF. The most sensitive detection approach involves the initial 253.7nm excitation followed by excitation of the 71S0–63P1 transition at 407.8nm. Fluorescence is observed on the 61P1–61S0 transition at 184.9nm. Using this approach, our limits of detection are 0.1ngm−3 with a 10s integration time in air. We have also examined the effects of saturation, quenching and line-width on detection sensitivity. We have used the pulsed laser photolysis–pulsed laser-induced fluorescence (PLP-PLIF) technique to study the kinetics of the reaction of elemental mercury with the hydroxyl radical under atmospheric conditions at 298K. We see no evidence for reaction and obtain an upper limit of 1.2×10−13cm3molecule−1s−1 for the rate coefficient.
    Journal of Photochemistry and Photobiology A Chemistry 01/2003; 157(2):247-256. · 2.42 Impact Factor
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    ABSTRACT: We have examined the sensitivity of sequential two photon laser induced fluorescence (LIF) detection of elemental mercury, Hg(0) in the gas phase. The most sensitive approach involves an initial laser excitation of the 6(3)P1-6(1)S0 transition at 253.7 nm, followed by excitation with a second laser to the 7(1)S0 level. Blue shifted fluorescence is observed on the 6(1)P1-6(1)S0 transition at 184.9 nm. The excitation scheme, involving sequential excitation of two atomic transitions, followed by detection of the emission from a third is extremely specific and precludes detection of anything other than atomic mercury. Using our 10 Hz laser system we have achieved a detection sensitivity of 0.1 ng m(-3) at a sampling rate of 0.1 Hz, i.e. averaging 100 laser shots at a pressure of one atmosphere in air. At low concentrations we sampled simultaneously with an automated mercury analyzer (Tekran 2537A), to ensure accuracy. We have examined the linearity of the technique, generating flows containing mercury concentrations between 1 and 10,000 ng m(-3) using a permeation tube and dynamic dilution, but relying on the concentrations given by the Tekran at low levels and the concentration calculated from dilution at high levels. We find that the detection is linear over the five orders of magnitude that we were able to vary the concentration. Our measured detection limits in He and Ar are much lower as these gases are inefficient fluorescence quenchers.
    Journal of Environmental Monitoring 07/2002; 4(3):339-43. · 2.09 Impact Factor
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    ABSTRACT: The kinetics of the recombination reaction, OH+NO2+(M)→HNO3 +(M) have been investigated by the pulsed laser photolysis−pulsed laser induced fluorescence (PLP−PLIF) technique in air, nitrogen, oxygen, and helium buffer gases at room temperature and as a function of pressure (30−700 Torr). Additional measurements in nitrogen at 273 K (100−700 Torr) are reported. The third-body efficiency of water vapor has also been investigated. Our values for the absolute rate coefficient in nitrogen at room temperature and at 273 K are in excellent agreement with the JPL 1994 recommendation but lie substantially above the current JPL 2000 recommendation. Our rate coefficients in helium agree with previous literature studies, suggesting that systematic errors are small. Oxygen is found to be about 20% less efficient than nitrogen, and we see no significant enhancement in recombination in the presence of water vapor. Our results suggest that formation of the pernitrous acid isomer cannot explain the discrepancies in the current experimental database.
    10/2001;
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    ABSTRACT: The pulsed laser photolysis–pulsed laser induced fluorescence (PLP–PLIF) technique has been used to study the reactions of OH with DMS and DMS-d6. The effective rate coefficient for the reaction of OH with DMS-d6 has been determined as a function of O2 partial pressure at 600 Torr total pressure in N2/O2 mixtures at 298 and 261 K and for both DMS and DMS-d6 at 240 K. Currently recommended rates are based on an empirical fit to a two-channel mechanism. This work shows that at low temperatures the currently recommended expression underestimates both the effective rate coefficient for reaction together with the branching ratio between addition and abstraction.
    Chemical Physics Letters 01/2001; 344(1):61-67. · 2.15 Impact Factor
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    ABSTRACT: The formation of O 1D from the photolysis of ozone has been observed at photolysis wavelengths between 305 and 375 nm and relative quantum yields for O 1D production have been determined. Ozone was photolyzed using a frequency doubled, optical parametric oscillator. O 1D was monitored indirectly, using laser induced fluorescence (LIF) detection of vibrationally excited OH as a ‘‘spectroscopic marker’’. Relative O 1D yields were measured from 305 to 375 nm at 295 K and from 305 to 340 nm at 273 K. The quantum yield decreases between 305 and 325 nm with a temperature dependence in the range between 310 and 325 nm. This is consistent with O 1D production via both spin-allowed and spin-forbidden processes. Between 325 and 375 nm a constant quantum yield of 0.064±0.006 was obtained suggesting production via an exclusively spin-forbidden process and indicating that absorption takes place to a single excited state which either predissociates, yielding O3P and O23Σ−, or crosses to another surface before dissociating to produce O 1D and O23Σ−.
    Physical Chemistry Chemical Physics 01/2000; 2(7):1421-1424. · 3.83 Impact Factor