1. Kinetics and Spectroscopy of the Gas Phase (CH 3 ) 2 S–Br Adduct V. Dookwah-Roberts 1, R.J.H. Lee 2, J.M. Nicovich 2, and P.H. Wine 1,2 1 School of Earth & Atmospheric Sciences 2 School of Chemistry & Biochemistry Georgia Institute of Technology 4th EAS Graduate Student Symposium, Atlanta GA, November 10 th 2006

2. MOTIVATION ● DMS (CH 3 SCH 3 ) accounts for 10-30 % of the total sulfur flux to the atmosphere. the total sulfur flux to the atmosphere. ● DMS oxidation impacts cloud formation over oceans => climate effects. oceans => climate effects. ● BrO x radicals represent one important DMS oxidant in the marine environment. oxidant in the marine environment.

3. Literature Summary: Br + DMS ↔ Br-DMS ● Wine et al., in NATO ASI Ser., Vol I7, Ed. by H. Niki & K.H. Becker, 1993, 385. Niki & K.H. Becker, 1993, 385. ● Ingham et al., J. Phys. Chem. A 1999, 103, 7199 ● Nakano et al., J. Phys. Chem. A 2001, 105, 11045

4. Goals of this Study ● 1 st study of adduct kinetics ●Map spectrum in region 300 – 500nm. Compare results with Ingham et al. and Nakano et al. ●Assess reactivity trends in reactions of weakly-bound halogen atom adducts with atmospheric gases.

5. Experimental Approach ● Laser flash photolysis − time−resolved UV−vis absorption spectroscopy ● T = 265 K; P = 200 Torr N 2 /O 2 ● Source of Br in all experiments: CF 2 Br 2 + hν(248 nm) → Br + CF 2 Br

6. Time−resolved absorption data 265 K, 200 Torr N 2, λ = 365 nm The observed absorption is coming from a product of Br + CH 3- S-CH 3 (almost certainly the CH 3 S(Br)CH 3 adduct).

7. Absorption Spectrum  at 338 nm is much smaller than found by Nakano et al. but spectrum agrees well with Ingham et al.

8. Radical − Radical Reaction Kinetics T = 265 K, P = 200 Torr N 2 [Br-DMS] / [Br] ~ 178 Slope (red line) gives 2k = (3.29 ± 0.04) x 10 −10 cm 3 molec −1 s −1 (Br-DMS + Br-DMS → products) (Br-DMS + Br-DMS → products) Average of 26 expts. like the one shown on the right gives 2k = (3.0 ± 0.3) x 10 −10 cm 3 molec −1 s −1 (uncertainty is 2σ, precision only).

9. Adduct + O 2 Reaction Kinetics T = 265 K; P = 200 Torr O 2 ; [DMS] = 1.6 x 10 15 per cm 3 ; [Br] 0 ≈ 1 x 10 13 per cm 3. Simulations suggest that upward curvature in the [Br-DMS] −1 vs. time plot would be observable if the Br-DMS + O 2 rate coefficient was > 1 x 10 −17 cm 3 molec −1 s −1.

10. Adduct + NO/NO 2 Reaction Kinetics Experimental conditions of low T (265 K), P (200 Torr N 2 ), low [Br] 0, and high [DMS] are employed to minimize interferences from radical − radical reactions and Br + NO x reactions.

11. species k O2 (10 -18 cm 3 molecule -1 s -1 ) k NO (10 -11 cm 3 molecule -1 s -1 ) k NO2 (10 -11 cm 3 molecule -1 s -1 ) references Br-DMSCl-DMSO CH 3 I-Cl C 2 H 5 I-Cl CS 2 -Cl Cl-DMS < 2 < 3 < 30 < 10 < 5 < 4 (1.3 ± 0.2) (1.2 ± 0.3) (2.0 ± 0.2) (2.2 ± 0.5) (1.2 ± 0.2) (2.6 ± 0.2) (2.1 ± 0.3) (3.5 ± 0.4) (3.9 ± 0.5) (1.3 ± 0.4) (2.7 ± 0.4) this work a bc Summary of Reaction Kinetics of Halogen Adducts with O 2, NO and NO 2 a. Kleissas, K.M.; Nicovich, J.M.; Wine, P.H. J. Photochem. In press. b. Dookwah-Roberts, V.; Soller, R.; Nicovich, J.M.; Wine, P.H. J. Photochem. 2005, 176, 114-123. c. Urbanski, S.P.; Wine, P.H. J. Phys. Chem. A 1999, 103, 10935-10944.

12. SUMMARY ●  max and max obtained agree well with Ingham et al. but  at 338 nm is a factor of 7 smaller than obtained by Nakano et al. ● Kinetic data obtained for 1 st time. ● Rate constants similar to other adducts studied eg. SCS-Cl, DMS-Cl, DMSO-Cl.

13. Future Directions ● Conduct pressure dependent study of BrO + DMS reaction kinetics. BrO + DMS reaction kinetics.

14. Acknowledgments Research Group Members (non-authors) Zhijun Zhao Dow Huskey Andrew Mudd Patrice Bell Katie Olsen Support $$$ NSF & NASA

15. Comparative Spectroscopy ________________________________________________________________________________________________________________________________ Adduct λ max (nm) FWHM (nm) σ max (10 −18 cm 2 ) a Adduct λ max (nm) FWHM (nm) σ max (10 −18 cm 2 ) a_____________________________________________________________________________________________________________________ SCS−Cl b 365 23 23 SCS−Cl b 365 23 23 480 85 3.9 480 85 3.9 (CH 3 ) 2 S−Cl c,d 340 75 35 (CH 3 ) 2 S−Cl c,d 340 75 35 (CH 3 ) 2 (O)S−Cl e 390 100 21 (CH 3 ) 2 S−Br f 365 75 27 (CH 3 ) 2 S−Br f 365 75 27________________________________________________________________________________________________________________________________ a Uncertainties are typically 30−40%. b Dookwah-Roberts, Soller, Nicovich, and Wine, J. Photochem. Photobiol. A: Chem., submitted (this work). c Urbanski & Wine, J. Phys. Chem. A 1999, 103, 10935. d Enami, Nakano, Hashimoto, Kawasaki, Aloisio, & Francisco, J. Phys. Chem. A, 2004, 108, 7785. e Wine, Nicovich, McKee, Kleissas, Parthasarathy, Pope, &Pegus, 18 th Intl. Symp. on Gas Kinetics, Bristol, UK, 2004, to be published. f Ingham, Bauer, Sander, Crutzen, & Crowley, J. Phys. Chem. A 1999, 103, 7199.

16. LFP−TRUVVAS Apparatus

17. Comparative Kinetics _________________________________________________________________________________________________________________ Adductk O2 a k NO a k NO2 a Adductk O2 a k NO a k NO2 a ______________________________________________________________________________________________________ ___________ SCS−Cl b < 5 x 10 -5 220 130 (CH 3 ) 2 S−Cl c < 4 x 10 −5 120 270 (CH 3 ) 2 S−Cl c < 4 x 10 −5 120 270 (CH 3 ) 2 (O)S−Cl d < 1 x 10 −5 150 190 (CH 3 ) 2 (O)S−Cl d < 1 x 10 −5 150 190 SCS−OH 0.29 e,f,g 7.3 g 420 g SCS−OH 0.29 e,f,g 7.3 g 420 g (CH 3 ) 2 S−OH 9.6 h,i (CH 3 ) 2 S−OH 9.6 h,i_________________________________________________________________________________________________________________ a Units are 10 −13 cm 3 molec −1 s −1. b Dookwah-Roberts, Soller, Nicovich & Wine, J. Photochem. Photobiol. A: Chem, submitted (this work). c Urbanski & Wine, J. Phys. Chem. A 1999, 103, 10935. d Wine, Nicovich, McKee, Kleissas, Parthasarathy, Pope, & Pegus, 18 th Intl. Symp. on Gas Kinetics, Bristol, UK, 2004, to be published. e Hynes, Wine, & Nicovich, J. Phys. Chem. 1988, 92, 3846. f Murrells, Lovejoy, & Ravishankara, J. Phys. Chem. 1999, 2381. g Diau & Lee, J. Phys. Chem. 1991, 95, 7726. h Hynes, Stoker, Pounds, McKay, Bradshaw, Nicovich, & Wine, J. Phys. Chem. 1995, 99, 16967. i Barone, Turnipseed, and Ravishankara, J. Phys. Chem. 1996, 100, 14694.