MOTIVATIONS : Atmospheric Chemistry

Troposphere Chemistry – Ozone Production

RO2 + NO → RO + NO2

NO2 → NO + O(3P)

O(3P) + O2 + M → O3 + M

M. J. Pilling, Comprehensive Chemical Kinetics, 35, 1(1997)

MOTIVATIONS : Low Temperature Combustion

Cavity Ringdown Absorption SpectroscopyCavity Ringdown Absorption Spectroscopy

Time

Inte

nsit

y

0

absorber

cL )/(0

R1

(a)

(b)ln

cL )/(R1

L=1mR=0.99%

0=34 s

A = nl

Leff=10 km

Sensitive

R

L

A = L/cabsorber - L/c0

Experimental Setup

Ringdown Cell

YAG 532 nm Sirah Dye Laser

H2 Raman Cell

PD

High Reflectivity Mirrors

ArF

193 nm

650 – 700 mJ 90 – 130 mJ

1 – 2 mJ

160 – 200 mJ

1.5 - 1.1 m

2nd Stokes

Filters

DCM & Rhodamine B/101

580 – 640 nm

cm-1

7300 7350 7400 7450 7500 7550 7600 7650 7700

pp

m

0

200

400

600

800

1000

0-0

photolysis off

photolysis on

Origin of the A2A - X2A Electronic Transition of CH3O2

Reaction*Initiation:

Precursor + hν R+(CO, Br , I, CO2) Production:

O2+R+M RO2+M Radical-Radical Losses:

R+R+M R2+MR+RO2 2RO

RO2+RO2 Products

*precursor for CH3 - acetone / methyl iodide

7300 7350 7400 7450 7500 7550 7600 7650 7700

Abs

orpt

ion

(ppm

)

0

100

200

300

400

500

600

700

800

0-0

cm-1

Origin of the A2A - X2A Electronic Transition of CH3O2

~/

M. B. Pushkarsky, S. J. Zalyubovsky, and T. A. Miller, J. Chem. Phys.  112, 10695 (2000)

MOTIVATIONS : Why C6H5O2 and How ?

The reaction of phenyl radical (C6H5) with molecular oxygen is postulated to impede the formation of soot inherent in hydrocarbon combustion, according to the following mechanism.

256HC

56 HCHC 56

O2

C6H5O2

Production of C6H5 radical from Acetophenone at 193 nm

3 Channels

C6H5COCH3 + hv

C6H5 + CH3CO (2)

C6H5CH3 + CO (3)

C6H5CO + CH3 (1)

C6H5COCH3 + hv

C6H5COCH3 + hv

(1) and (2) have comparable cross sections. Cross section for channel (3) is estimate to be less than 0.1 % of those processes (1) and (2). 30 – 50 % of primary C6H5CO further decomposes, yielding secondary products C6H5 + CO and

CH3 + CO respectively

Zhao, H.-Q. et al. Journal of Chemical Physics (1997), 107(18), 7230-7241.

cm-1

7300 7400 7500 7600 7700

pp

m

0

50

100

150

200

cm-1

7300 7400 7500 7600 7700

MeO

2 R

efer

ence

Sig

nal

0

500

1000

1500

2000

pp

m

0

50

100

150

200

Photolysis of acetophenone at 193 nm

Bond Origin

Acetophenone at 193 nm(1)Acetone at 193 nm

(1) M. B. Pushkarsky, S. J. Zalyubovsky, and T. A. Miller, J. Chem. Phys.  112, 10695 (2000)

Comparaison with other precursors

cm-1

7300 7400 7500 7600 7700

MeO

2 R

efer

ence

Sig

nal

0

500

1000

1500

2000

ppm

0

50

100

150

200

Acetophenone at 193 nm

(1)Acetone at 193 nm

Bromobenzene at 193 nm

PhO2

MeO2

Frequency (cm-1)

7300 7400 7500 7600 7700 7800 7900 8000

Ab

so

rptio

n (

pp

m)

0

20

40

60

80

100

120

140

Photolysis of acetophenone at 193 nm

Band Origin

MeO2

PhO2

PhO2

Photolysis of acetophenone at 193 nm

O-O Stretch

Frequency (cm-1)

8340 8360 8380 8400 8420 8440 8460 8480 8500 8520 8540

Ab

so

rptio

n (

pp

m)

0

10

20

30

40

50

60

70

PhO2MeO2

MeO2

Frequency (cm-1)

8340 8360 8380 8400 8420 8440 8460 8480 8500 8520 8540

Ab

so

rptio

n (

pp

m)

0

10

20

30

40

50

60

70

Tentative assignment

O-O stretch

1401

1201

Tentative assignment

Frequency (cm-1)

7300 7400 7500 7600 7700 7800 7900 8000

Ab

so

rptio

n (

pp

m)

0

20

40

60

80

100

120

140

2301

cm-1

7420 7440 7460 7480 7500 7520 7540 7560 7580 7600 7620

pp

m

0

20

40

60

80

100

Tentative assignment

Zoom

000

3311

3322

3333

cm-1

7420 7440 7460 7480 7500 7520 7540 7560 7580 7600 7620

pp

m

0

20

40

60

80

100

Assignment

3301

Conclusion and Future Work

~~

• We have observed the A2A' –X2A" electronic transition of phenyl peroxy radical.

• Assignment has been done.

• Studying other unsaturated peroxy radicals and other peroxy radicals (C5H11O2).

~~