Research ArticleChemistry

Direct measurements of DOCO isomers in the kinetics of OD + CO

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Science Advances  12 Jan 2018:
Vol. 4, no. 1, eaao4777
DOI: 10.1126/sciadv.aao4777
  • Fig. 1 The OH + CO reaction PES with energies in kilojoules per mole.

    The colored PES in the background depicts the HOCO isomer potential energy wells along the H–O–C–O dihedral angle (parallel to page) and O–H bond length (perpendicular to page).

  • Fig. 2 Spectroscopy of DOCO isomers.

    (A) Full cis-DOCO spectrum (top). The data and simulation are given by positive and negative absorbances, respectively. The color codes are as follows: blue, cis-DO12CO; red, cis-DO13CO; green, OD; gray, D2O. For clarity, only the simulated cis-DO12CO and cis-DO13CO are shown for comparison with experimental results in the zoomed-in bottom panels, where the strongest Q branches are located. (B) Trans-DOCO spectrum (black). Simulated trans-DOCO (brown), OD (green), and D2O (gray) are shown as inverted absorbances. The detection spectral regions are 2400 to 2850 cm−1 (OD), 2450 to 2650 cm−1 (cis-DOCO) (A), 2640 to 2720 cm−1 (trans-DOCO) (B), and 2380 to 2445 cm−1 (CO2). Data in (A) and (B) were obtained by integrating from t = 0 to 200 μs at a 100-μs camera integration time.

  • Fig. 3 Time traces of reaction components and the formation rates for the sum of DOCO isomers.

    (A) Time dependence of reactant OD (green circles), intermediates cis-DO12CO (blue squares) and trans-DOCO (brown diamonds), and product CO2 (purple triangles) obtained from fitting full experimental spectra for a sequence of time windows after the initiation of the reaction. Quantities in parenthesis are multiplicative factors used to scale the traces to fit on a single plot. The camera integration time is 20 μs for OD, cis-DOCO, and trans-DOCO and 50 μs for CO2. Each time point corresponds to ≈400 averaged spectra. The error bars are from uncertainties in the fit and the measured densities of the gases. The dashed and dotted lines are fits of eq. S4 for OD, Eq. 6 for trans- and cis-DOCO, and eq. S8 for CO2 using values measured from this work. (B) k1a,sum is plotted as a function of CO, whereas [N2] is held constant at 8.9 × 1017 molecules cm−3. (C) k1a,sum is plotted as a function of N2, whereas [CO] is held constant at 5.6 × 1017 molecules cm−3. In both plots, [D2] and [O3] are fixed at 1.4 × 1017 and 2 × 1015 molecules cm−3, respectively. The red dashed lines show the fits obtained from a multidimensional linear regression procedure described in the main text. Data in (B) and (C) were obtained at a 50-μs camera integration time. The error bars in (B) and (C) represent uncertainties from fits to Eqs. 8 and 9 and the measured densities of the gases.

  • Fig. 4 DOCO formation and isomerization kinetics.

    (A) Ratio of [trans-DOCO] to [cis-DOCO] as a function of time for different CO concentrations. The CO concentrations are 5.6 × 1017, 6.0 × 1017, 6.4 × 1017, 6.7 × 1017, and 7.1 × 1017 molecules cm−3 for blue squares, red circles, black diamonds, cyan hexagons, and green triangles, respectively. For these experiments, [N2], [D2], and [O3] were fixed to 8.9 × 1017, 1.4 × 1017, and 2 × 1015 molecules cm−3, respectively. The arbitrary y-axis offsets of −5, −2.5, 0, +2.5, and +5, respectively, are added for ease of viewing. At high [CO] (>6.4 × 1017 molecules cm−3), all curves reach the same asymptotic value within experimental uncertainties. The dashed lines are fits of the rate equation model to the data. Data were obtained at a 20-μs camera integration time. The error bars represent uncertainties from the spectral fit and measured densities of gases. (B) Fitted isomerization rate coefficients for cistrans (Embedded Image; blue squares) and transcis (Embedded Image; red circles). The ratio of Embedded Image as a function of [CO] is given in the inset. (C) Fitted effective bimolecular formation rate coefficients (k1a) for trans-DOCO (k1a,trans; black diamonds) and cis-DOCO (k1a,cis; green squares). The ratio of the formation rate coefficients k1a,trans/k1a,cis as a function of [CO] is given in the inset. The error bars in (B) and (C) represent uncertainties from the individual parameter variance and covariance between k1a,sum and kiso.

Supplementary Materials

  • Supplementary material for this article is available at http://advances.sciencemag.org/cgi/content/full/4/1/eaao4777/DC1

    section S1. cis-DOCO isotope shift and spectral parameters

    section S2. k1a,sum fitting

    section S3. Theoretical calculations for OD + CO

    section S4. k1 for OD + CO as a function of N2

    table S1. Experimental spectral features for cis-DO12CO and cis-DO13CO and their rovibrational assignments.

    table S2. Summary of spectral parameters for cis-DO12CO and cis-DO13CO.

    table S3. Comparison of experimental and theoretical isotopic shifts for cis-DOCO.

    table S4. Summary of statistical and systematic errors for k1a,sum.

    table S5. Summary of fitted rate coefficients.

    fig. S1. Variation of rloss,sum with O3 concentration.

    fig. S2. Variation of k1a,sum with D2 concentration.

    fig. S3. Calculated cis/trans isomerization rates for DOCO isomers using SCTST and 2D master equations.

    fig. S4. Measured k1 comparison with previous works.

  • Supplementary Materials

    This PDF file includes:

    • section S1. cis-DOCO isotope shift and spectral parameters
    • section S2. k1a,sum fitting
    • section S3. Theoretical calculations for OD + CO
    • section S4. k1 for OD + CO as a function of N2
    • table S1. Experimental spectral features for cis-DO12CO and cis-DO13CO and their rovibrational assignments.
    • table S2. Summary of spectral parameters for cis-DO12CO and cis-DO13CO.
    • table S3. Comparison of experimental and theoretical isotopic shifts for cis-DOCO.
    • table S4. Summary of statistical and systematic errors for k1a,sum.
    • table S5. Summary of fitted rate coefficients.
    • fig. S1. Variation of rloss,sum with O3 concentration.
    • fig. S2. Variation of k1a,sum with D2 concentration.
    • fig. S3. Calculated cis/trans isomerization rates for DOCO isomers using SCTST and 2D master equations.
    • fig. S4. Measured k1 comparison with previous works.

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