doi:10.1016/j.jphotochem.2006.08.020 
Copyright © 2006 Elsevier B.V. All rights reserved.
Spectroscopy and kinetics of the gas phase addition complex of atomic chlorine with dimethyl sulfoxide
K.M. Kleissasa, 1, J.M. Nicovicha and P.H. Winea, b, 
, 
aSchool of Chemistry and Biochemistry, Georgia Institute of Technology, Atlanta, GA 30332-0400, United States
bSchool of Earth and Atmospheric Sciences, Georgia Institute of Technology, Atlanta, GA 30332-0340, United States
Received 5 July 2006;
revised 4 August 2006;
accepted 4 August 2006.
Available online 1 September 2006.
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Abstract
Time-resolved UV–vis absorption spectroscopy has been coupled with 248 nm 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 296 K. CH3(Cl)S(O)CH3 is found to possess a strong absorption band with λmax = 394 nm and σmax = (4.0 ± 1.4) × 10−17 cm2 molecule−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 × 10−18 cm3 molecule−1 s−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 10−11 cm3 molecule−1 s−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.
Keywords: DMSO; Sulfur chemistry; Atmospheric chemistry; Radical spectroscoopy; 3-Electron bond
Fig. 1. A typical absorbance (base e) temporal profile observed following laser flash photolysis of Cl2CO/DMSO/N2 mixtures at P = 50 Torr. Concentrations in units of 1013 molecules cm−3 are [Cl2CO] = 158, [Cl]0 ≈ 0.5, and [DMSO] = 61.1. The solid line is obtained from a nonlinear least squares fit to the sum of an exponential rise and an exponential decay. The best fit appearance (ka) and disappearance (kd) rate coefficients in units of s−1 are ka = 49,600 and kd = 714.
Fig. 2. Plot of ka vs. [DMSO] for data obtained at P = 50 Torr N2. The solid line is obtained from a linear least squares analysis; its slope gives the second order rate coefficient k1 = (6.52 ± 0.33) × 10−11 cm3 molecule−1 s−1 where the uncertainty is 2σ and represents precision only. The open circle is the data point obtained from the data shown in Fig. 1.
Fig. 3. Absorption spectrum of the CH3(Cl)S(O)CH3 adduct at a spectral resolution of 3.7 nm.
Fig. 4. Typical CH3(Cl)S(O)CH3 absorbance temporal profile observed following 248 nm laser flash photolysis of Cl2CO/DMSO/N2 mixtures. Experimental conditions: P = 300 Torr; concentrations in units of 1015 molecules cm−3 = 12.9 Cl2CO and 1.82 DMSO. The solid line is obtained from a linear least squares analysis; its slope gives 2k3 = (6.29 ± 0.02) × 10−11 cm3 molecule−1 s−1 under the assumption of scenario (1) described in the text, where the uncertainty is 2σ and represents precision only.
Fig. 5. CH3(Cl)S(O)CH3 absorbance temporal profiles in N2 and O2 plotted as ln A (base e) vs. time. Experimental conditions: P = 300 Torr and concentrations in units of 1013 molecules cm−3 = 47 Cl2CO, 0.16 Cl0, and 105 DMSO. The solid lines are obtained from linear least squares analyses of all data at times 3.0–15.0 ms after the laser flash; their slopes give apparent pseudo-first order decay rates of 90.5 ± 3.5 s−1 for the N2 experiment and 89.4 ± 3.6 s−1 for the O2 experiment (uncertainties are 2σ and represent precision only). For the sake of clarity, the O2 data are displaced upward on the vertical scale by 1 unit of ln A.
Fig. 6. Typical absorbance (base e) temporal profile observed following 248 nm laser flash photolysis of Cl2CO/DMSO/NOx/N2 mixtures. Experimental conditions: NOx = NO2; P = 300 Torr; concentrations in units of 1013 molecules cm−3 are [DMSO] = 113, [Cl2CO] = 390, [Cl]o ≈ 1.0, and [NO2] = 18.3. The solid line is obtained from a linear least squares analysis of the ln A vs. time data using only data where A < 0.012; its slope gives the pseudo-first order decay rate k′ = 3810 ± 80 s−1 where the uncertainty is 2σ and represents precision only.
Fig. 7. Plots of pseudo-first-order adduct decay rate (k′) vs. [NOx] for data obtained at pressures of 30 and 300 Torr N2. Circles are NO2 data points and squares are NO data points. Filled symbols are 30 Torr data and open symbols are 300 Torr data; the open symbol with an “×” in the middle is the data point obtained from the temporal profile shown in Fig. 6. Solid lines are obtained from linear least-squares analyses of all NO and NO2 data, respectively; their slopes give the following bimolecular rate coefficients in units of 10−11 cm3 molecule−1 s−1: k9 = 1.20 ± 0.19 and k10 = 2.06 ± 0.18; uncertainties are 2σ and represent precision only.
Table 1.
Spectroscopic properties of halogen atom adducts with (CH3)2SO (DMSO) and (CH3)2S (DMS)
a Units are
λmax (nm);
σmax (10
−17 cm
2 molecule
−1, base e); FWHM (cm
−1).
b All spectral shapes are approximated by a Gaussian function when plotted as
σ vs.
λ. FWHM: full width at half maximum.
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10 s−1 from modelling the experimental profiles of the reactant and products.
