Kinetics and Spectroscopy of the Kinetics and Spectroscopy of the

Gas Phase (CHGas Phase (CH33))22SS––Br AdductBr Adduct

V. Dookwah-RobertsV. Dookwah-Roberts11, R.J.H. Lee, R.J.H. Lee22,,

J.M. NicovichJ.M. Nicovich22, and P.H. Wine, and P.H. Wine1,21,2

11 School of Earth & Atmospheric Sciences School of Earth & Atmospheric Sciences

22 School of Chemistry & Biochemistry School of Chemistry & Biochemistry

Georgia Institute of TechnologyGeorgia Institute of Technology

4th EAS Graduate Student Symposium, Atlanta GA, November 104th EAS Graduate Student Symposium, Atlanta GA, November 10 thth 2006 2006

MOTIVATIONMOTIVATION

●● DMS (CHDMS (CH33SCHSCH33) accounts for 10-30 % of ) accounts for 10-30 % of

the total sulfur flux to the atmosphere.the total sulfur flux to the atmosphere.

●● DMS oxidation impacts cloud formation overDMS oxidation impacts cloud formation over

oceans => climate effects.oceans => climate effects.

●● BrOBrOxx radicals represent one important DMS radicals represent one important DMS

oxidant in the marine environment.oxidant in the marine environment.

Literature Summary: Br + DMS ↔ Br-DMSLiterature Summary: Br + DMS ↔ Br-DMS

●● Wine et al., in Wine et al., in NATO ASI Ser., Vol I7, NATO ASI Ser., Vol I7, Ed. by H. 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 Ingham et al., J. Phys. Chem. A 1999, 103, 7199

● ● Nakano et al., J. Phys. Chem. A 2001, 105, 11045 Nakano et al., J. Phys. Chem. A 2001, 105, 11045

Goals of this StudyGoals of this Study

●● 11stst study of adduct kinetics study of adduct kinetics

●● Map spectrum in region 300 – 500nm. Compare results Map spectrum in region 300 – 500nm. Compare results with Ingham et al. and Nakano et al.with Ingham et al. and Nakano et al.

●● Assess reactivity trends in reactions of weakly-bound Assess reactivity trends in reactions of weakly-bound halogen atom adducts with atmospheric gases.halogen atom adducts with atmospheric gases.

Experimental ApproachExperimental Approach

●● Laser flash photolysis − time−resolved Laser flash photolysis − time−resolved

UV−vis absorption spectroscopyUV−vis absorption spectroscopy

●●T = 265 K; P = 200 Torr NT = 265 K; P = 200 Torr N22/O/O22

●● Source of Br in all experiments:Source of Br in all experiments:

CFCF22BrBr22 + h + hνν(248(248 nm) →nm) → Br + CFBr + CF22BrBr

Time−resolved absorption dataTime−resolved absorption data

265 K, 200 Torr265 K, 200 Torr NN22, , λλ = 365 nm = 365 nm

The observed absorption is coming from a product of Br + CH3-S-CH3 (almost certainly the CH3S(Br)CH3 adduct).

16

14

12

10

8

6

4

Ab

sorb

ance

x 1

000

400300200100

Time (s)

70

60

50

40

30

20

10

0

k a (

103 s

-1)

76543210

[DMS] (1014

molecules cm-3

)

9.12 x 10-11

Absorption SpectrumAbsorption Spectrum

at 338 nm is much smaller than found by Nakano et al.

but spectrum agrees well with Ingham et al.

30

25

20

15

10

5

0

(1

0-18

cm2

mo

lecu

le-1

)

550500450400350

Wavelength (nm)

Our data

Ingham et al.

Radical − Radical Reaction KineticsRadical − Radical Reaction Kinetics

T = 265 K, P = 200 Torr NT = 265 K, P = 200 Torr N22

[Br-DMS[Br-DMS] / [Br] ~ ] / [Br] ~ 178178

Slope (red line) givesSlope (red line) gives

2k = (3.29 2k = (3.29 ±± 0.04) x 10 0.04) x 10−−1010 cm cm33molecmolec−−11ss−−11

((Br-DMSBr-DMS + + Br-DMSBr-DMS → products) → products)

Average of 26 expts. like the one

shown on the right gives

2k = (3.0 ± 0.3) x 10−10 cm3molec−1 s−1

(uncertainty is 2σ, precision only).

1.0

0.8

0.6

0.4

0.2

0.0

[Br-

DM

S]-1

(10

-12cm

3m

ole

cule

-1)

1.00.80.60.40.20.0

Time (ms)

Adduct + OAdduct + O22 Reaction Kinetics Reaction Kinetics

T = 265 K; P = 200 Torr OT = 265 K; P = 200 Torr O22; [DMS] = 1.6 x 10; [DMS] = 1.6 x 101515 per cm per cm33; [Br]; [Br]00 ≈ 1 x 10 ≈ 1 x 101313 per cm per cm33..

Simulations suggest that upward curvature in the [Br-DMS]Simulations suggest that upward curvature in the [Br-DMS]−1−1 vs. time plot would be vs. time plot would be

observable if the Br-DMS + Oobservable if the Br-DMS + O22 rate coefficient was > 1 x 10 rate coefficient was > 1 x 10−17−17 cm cm33molecmolec−1−1ss−1−1..

1.4

1.2

1.0

0.8

0.6

0.4

0.2

0.0[Br-

DM

S]-1

(10

-12 c

m3 m

ole

cule

-1)

2.01.51.00.50.0Time (ms)

01E-17

5E-17

3E-17

Br-DMS + O2

Adduct + NO/NOAdduct + NO/NO22 Reaction KineticsReaction KineticsExperimental conditions of low T (265 K), P (200 Torr N2), low [Br]0, and high [DMS] are employed to minimize interferences from radical − radical reactions and Br + NOx reactions.

-9

-8

-7

-6

-5

-4

ln A

bs

orb

an

ce

250200150100500Time (s)

Br-DMS + NO

4

3

2

1

0

k d (

104 s

-1)

2520151050

[NOx] (1014

molecules cm-3

)

NO2

NO

2.6 x 10-11 1.3 x 10

-11

speciesspecies

kkO2O2

(10(10-18-18 cm cm33 molecule molecule-1-1 s s-1-1))

kkNONO

(10(10-11-11 cm cm33 molecule molecule-1-1 s s-1-1))

kkNO2NO2

(10(10-11-11 cm cm33 molecule molecule-1-1 s s-1-1)) referencesreferences

Br-DMSBr-DMS

Cl-DMSOCl-DMSO

CHCH33I-ClI-Cl

CC22HH55I-ClI-Cl

CSCS22-Cl-Cl

Cl-DMSCl-DMS

< 2 < 2

< 3< 3

< 30< 30

< 10< 10

< 5< 5

< 4< 4

(1.3 (1.3 ± 0.2)± 0.2)

(1.2 (1.2 ± 0.3)± 0.3)

(2.0 (2.0 ± 0.2)± 0.2)

(2.0 (2.0 ± 0.2)± 0.2)

(2.2 (2.2 ± 0.5)± 0.5)

(1.2 (1.2 ± 0.2)± 0.2)

(2.6 (2.6 ± 0.2)± 0.2)

(2.1 (2.1 ± 0.3)± 0.3)

(3.5 (3.5 ± 0.4)± 0.4)

(3.9 (3.9 ± 0.5)± 0.5)

(1.3 (1.3 ± 0.4)± 0.4)

(2.7 (2.7 ± 0.4)± 0.4)

this workthis work

aa

this workthis work

this workthis work

bb

cc

Summary of Reaction Kinetics of Summary of Reaction Kinetics of Halogen Adducts with OHalogen Adducts with O22, NO and NO, NO and NO22

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.

SUMMARYSUMMARY

●● maxmax and and maxmax obtained agree well with obtained agree well with

Ingham et al. but Ingham et al. but at 338 nm is a factor of at 338 nm is a factor of 7 smaller than obtained by Nakano et al. 7 smaller than obtained by Nakano et al.

●● Kinetic data obtained for 1Kinetic data obtained for 1stst time. time.

●● Rate constants similar to other adducts Rate constants similar to other adducts studied eg. SCS-Cl, DMS-Cl, DMSO-Cl. studied eg. SCS-Cl, DMS-Cl, DMSO-Cl.

Future DirectionsFuture Directions

●● Conduct pressure dependent study of Conduct pressure dependent study of

BrO + DMS reaction kinetics.BrO + DMS reaction kinetics.

AcknowledgmentsAcknowledgments

Research Group Members (non-authors)Research Group Members (non-authors)

Zhijun Zhao Dow HuskeyZhijun Zhao Dow Huskey Andrew Mudd Andrew Mudd

Patrice BellPatrice Bell Katie Olsen Katie Olsen

Support $$$Support $$$

NSF & NASANSF & NASA

Comparative SpectroscopyComparative Spectroscopy

________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________

AdductAdduct λλmax max (nm)(nm) FWHM (nm) FWHM (nm) σσmax max (10(10−18−18 cm cm22) ) aa

__________________________________________________________________________________________________________________________________________________________________________________________________________________________________________

SCS−Cl SCS−Cl bb 365 365 23 23 23 23 480480 85 85 3.9 3.9

(CH(CH33))22S−Cl S−Cl c,dc,d 340 340 75 75 35 35

(CH(CH33))22(O)S−Cl (O)S−Cl ee 390 390 100 100 21 21

(CH(CH33))22S−Br S−Br ff 365 365 75 75 27 27

________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________

a a Uncertainties are typically 30−40%.Uncertainties are typically 30−40%.b b Dookwah-Roberts, Soller, Nicovich, and Wine, Dookwah-Roberts, Soller, Nicovich, and Wine, J. Photochem. Photobiol. A: ChemJ. Photochem. Photobiol. A: Chem., submitted (this work).., submitted (this work).c c Urbanski & Wine, Urbanski & Wine, J. Phys. Chem. A J. Phys. Chem. A 19991999, , 103103, 10935., 10935.dd Enami, Nakano, Hashimoto, Kawasaki, Aloisio, & Francisco, Enami, Nakano, Hashimoto, Kawasaki, Aloisio, & Francisco, J. Phys. Chem. AJ. Phys. Chem. A, , 20042004, , 108108, 7785., 7785.e e Wine, Nicovich, McKee, Kleissas, Parthasarathy, Pope, &Pegus, 18Wine, Nicovich, McKee, Kleissas, Parthasarathy, Pope, &Pegus, 18 thth Intl. Symp. on Gas Kinetics, Bristol, UK, 2004, to Intl. Symp. on Gas Kinetics, Bristol, UK, 2004, to

be published.be published.ff Ingham, Bauer, Sander, Crutzen, & Crowley, Ingham, Bauer, Sander, Crutzen, & Crowley, J. Phys. Chem. AJ. Phys. Chem. A 1999 1999, , 103103, 7199., 7199.

FM

FM

PMTPG MIX

ING

CE

LL

REACTION CELL

EXCIMER LASER

Cl2CO/N2

N2 or O2

CS2

NO/NO2/ N2

Cl2CO MONITOR

FM

FM

OSCILLOSCOPE

COMPUTER

PMT

ARC LAMP

MONOCHROMATOR

HV

PM

T

BPF

TO PUMP

CS2 MONITOR

Zn LAMPPMT

BPF

COOLANT out

COOLANT in

Zn LAMP

TP TP

HR 248

HR 248

LFP−TRUVVASApparatus

Comparative KineticsComparative Kinetics

__________________________________________________________________________________________________________________________________________________________________________________________________________________________________

AdductAdduct kkO2O2aa

kkNONOaa k kNO2NO2

aa

__________________________________________________________________________________________________________________________________________________________________________________________________________________________________

SCS−Cl SCS−Cl bb < 5 x 10 < 5 x 10-5-5 220 220 130 130

(CH(CH33))22S−Cl S−Cl cc < 4 x 10 < 4 x 10−5−5 120 120 270 270

(CH(CH33))22(O)S−Cl (O)S−Cl dd < 1 x 10 < 1 x 10−5−5 150150 190 190

SCS−OH SCS−OH 0.29 0.29 e,f,ge,f,g 7.3 7.3 gg 420 420 g g

(CH(CH33))22S−OHS−OH 9.6 9.6 h,i h,i

__________________________________________________________________________________________________________________________________________________________________________________________________________________________________

a a Units are 10Units are 10−13 −13 cmcm3 3 molecmolec−1 −1 ss−1−1..

b b Dookwah-Roberts, Soller, Nicovich & Wine, Dookwah-Roberts, Soller, Nicovich & Wine, J. Photochem. PhotobiolJ. Photochem. Photobiol. . A: Chem, A: Chem, submitted (this work). submitted (this work). c c Urbanski & Wine, Urbanski & Wine, J. Phys. Chem. A J. Phys. Chem. A 19991999, , 103103, 10935. , 10935. d d Wine, Nicovich, McKee, Kleissas, Parthasarathy, Pope, & Pegus, 18Wine, Nicovich, McKee, Kleissas, Parthasarathy, Pope, & Pegus, 18thth Intl. Symp. on Gas Kinetics, Bristol, UK, 2004, to be published. Intl. Symp. on Gas Kinetics, Bristol, UK, 2004, to be published.e e Hynes, Wine, & Nicovich, Hynes, Wine, & Nicovich, J. Phys. Chem. J. Phys. Chem. 19881988, , 9292, 3846. , 3846. f f Murrells, Lovejoy, & Ravishankara, Murrells, Lovejoy, & Ravishankara, J. Phys. Chem. J. Phys. Chem. 1999, 1999, 2381.2381.g g Diau & Lee, Diau & Lee, J. Phys. Chem. J. Phys. Chem. 19911991, , 9595, 7726., 7726.h h Hynes, Stoker, Pounds, McKay, Bradshaw, Nicovich, & Wine, Hynes, Stoker, Pounds, McKay, Bradshaw, Nicovich, & Wine, J. Phys. Chem.J. Phys. Chem. 19951995, , 9999, 16967., 16967.i i Barone, Turnipseed, and Ravishankara, Barone, Turnipseed, and Ravishankara, J. Phys. Chem. J. Phys. Chem. 19961996, , 100100, 14694., 14694.