THE OBSERVATIONS ON THE SPECTRUM GENERATED BY

PHOTOLYSIS OF CH2I2/O2 MIXTURE IN THE NEAR INFRARED REGION

Neal Kline, Meng Huang, and Terry A. Miller

Department of Chemistry and BiochemistryThe Ohio State University

BackgroundCriegee Intermediate

First proposed by Rudolf Criegee in 1949 as intermediate in ozonolysis of alkenes.Formed in the atmosphere and utilized heavily in organic chemistry to functionalize double bonds.Large amounts of research have been focused on the Criegee intermediate recently.

Background transition of the Criegee Intermediate

1A’

3A’

1A1

3A2

a. Harding, L. B. and Goddard III, W. A. J. Am. Chem. Soc. 1978, 100, 7180-7188.b. Wadt, W. R. and Goddard III, W. A. J. Am. Chem. Soc. 1975, 97, 3004-3021.

C=1s22s22p2

O=1s22s22p4

9530 cm-1

H

H

CO

O

H

H

OO

O

Sirah dye laser570-705 nm Nd:YAG: 532 nm

Raman cell (H2, 300 psi)

2nd Stokes:6000-9000 cm-1

Room Temperature Cavity Ring-Down Spectroscopy (CRDS) Setup

20 Hz~600 mJ/pulse

~70-80mJ/pulse

~1-2mJ/pulse

Photolysis:Excimer LaserKrF, 248 nm

HighlyReflective

Mirror(99.995 %)

HighlyReflective

Mirror(99.995 %)

Preparing the Molecule

Photolyze diiodomethane at 248 nm, one iodine atom dissociates. CH2I radical reacts with oxygen to give CH2IOO. CH2IOO then dissociates I atom to give CH2OO.a

We observed our spectrum under conditions of 86.0 torr total pressure (84.9 torr N2, 0.1 torr CH2I2, 1.0 torr O2) ,which is the same conditions as Y. P. Lee. b

a. Oliver Welz et al., Science, 335 204, 2012;b. Su, Y.; Huang, Y.; Witek, H. A. and Lee, Y. P. Science 2013, 340, 174.

C

H I

HIH

248 nmC

H

HI

+ I

CH2

O

OO2

+ 2ICH2IOO

H2OContamination

Iodine atom2P1/22P3/2

Precursor Absorption

Precursor Absorption

875 cm-1, Typical OO Stretch FrequencyExperimental Spectrum

~𝑎−~𝑋

~𝐴−~𝑋

Comparison of the Spectra for CH2XOO Radicals

- T00 Frequency

6908 cm-1

6817 cm-1

6799 cm-1

7383 cm-1

Good electronic structure calculations – FD07,DawesVibrational spectral analysis– FD06

Wavenumber(cm-1)

Carrier Determination Using Chemistry

C

H I

HIH

248 nmC

H

HI

+ I

CH2

O

OO2

+ 2ICH2IOO

a. Huang, H.; Eskola, A.; Taatjes, C. A. J. Phys. Chem. Lett. 2012, 3, 3399.

Mechanism requires libration of I upon reaction of CH2I+O2. Photolysis of CH2I2 with O2 present shows a nearly 50% increase in I atom signal compared to the photolysis without O2

SO2 is effective Criegee intermediate scavenger and reacts very quicklya,b,c, however reacts very slowly with peroxy radicalsd,e.

a. D. Stone, M. Blitz, L. Daubney, T. Ingham, and P. Seakins. Phys. Chem. Chem. Phys., 2013,15, 19119-19124.b. L. Sheps. J. Phys. Chem. Lett., 2013, 4, 4201-4205.c. O. Welz, J. D. Savee, D. L. Osborn, S. S. Vasu, C. J. Percival, D. E. Shallcross, and C. A. Taatjes. Science, 2012, 335, 204-207.d. P. D. Lightfoot, R. A. Cox, J. N. Crowley, M. Destriau, G. D. Hayman, M. E. Jenkin, M. J. Rossi, and J. Troe. Atmos. Chem. Phys., 2006, 6, 3625-4055.e. C. S. Kan, J. G. Calvert, and J. H. Shaw. J. Phys. Chem., 1981,85, 1126-1132.

3.9 x 10-11 cm3molec-1s-1

CH2O2 + SO2 SO3+CH2O

≤1 x 10-16 cm3molec-1s-1

SO2SO3+CH3O

CH3O2 +CH3O2SO2

Kinetics

Experimental Spectrum of CH2ClOO with SO2

Experimental Spectrum of CH2BrOO with SO2

Experimental Spectrum of the Carrier Generated by CH2I2/O2 mixed with SO2

Self Reaction?

Reaction Mechanism?

+SO2

CH2IO2 + CH2IO2 → 2CH2IO + O2

CH2O2 + CH2O2 → 2CH2O + O2

SummaryWe measured the spectrum generated by photolysing CH2I2 precursor mixed with O2 in the NIR region with cavity ringdown spectroscopy(CRDS). Spectra evidence show that the carrier of the spectrum is likely to be CH2IOO. The - electronic transitions of CH2BrOO and CH2ClOO were obtained with CRDS in the similar region, which shows some similarities and difference to the spectrum of unknown carrier.Kinetics evidence show that the carrier of the spectrum is suggestive to be CH2OO, but not definitive. The reaction of the SO2 with the carrier of the spectrum was studied. The spectrum of the unknown carrier has a significant decrease in intensity after mixing the precursor with SO2, while the CH2BrOO and CH2ClOO are not affected by SO2. Quantitative analyses in kinetics are also necessary to make the conclusion.

Dr. Terry A. MillerDr. Neal D. KlineDr. Dmitry MelnikDr. Mourad RoudjaneHenry Tran

Dr. Richard DawesPhalgun Lolur

KineticsIf we follow Y. P. Lee’s mechanism, and our upper estimates of the initial concentration of CH2I and iodine atoms at 1.0E+15, then the expected half-life time for Criegee is ~ 11 microseconds and for CH2IO2 is about 24 microseconds. The measured value is about 5 microseconds, which makes it look more like Criegee rather than peroxy.

12

2 2 2 213

2 2 2 211

2 2 2 2 2 211

2 2 2 2 2 25

2 2

2 2 2 2

2 2 2 2

2 2 2

2 2 2

1.04 10

4.6 10

8 1029 10210

5.7 1

CH I O CH O ICH I O CH O ICH O CH O CH O OCH IO CH IO CH IO OCH IO CH O ICH O I CH I OCH O I CH IOCH IO I CH IO IOCH O I CH O IOIO IO products

11

11

11

12

10

0

2.6 10

4 10

9 10

1.510

W.-L. Ting, C.-H. Chang, Y.-F. Lee, H. Matsui, Y.-P. Lee*, and Jim J.-M. Lin*, J. Chem. Phys. 141, 104308 (2014).R. Atkinson, el al., Atmos. Chem. Phys. 7, 981 (2007)T. Gravestock, M. Blitz, W. Bloss, and D. E. Heard, ChemPhysChem 11, 3928 (2010)

Time, s10 15 20 25 30

ppm

/pas

s

0

5

10

15

20

25

30

Kinetics

0.5 Torr of SO2 would “kill” Criegee almost immediately

Even if peroxy does not directly react with SO2, its temporal profile shows faster decay with the addition of SO2. When Criegee depletes faster, the peroxy replenishment channel quenches.

2 2 2 2 3CH IO SO CH IO SO 121.5 100

kk