motivations : atmospheric chemistry
DESCRIPTION
MOTIVATIONS : Atmospheric Chemistry. Troposphere Chemistry – Ozone Production RO 2 + NO → RO + NO 2 NO 2 → NO + O( 3 P) O( 3 P) + O 2 + M → O 3 + M. MOTIVATIONS : Low Temperature Combustion. - PowerPoint PPT PresentationTRANSCRIPT
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).
~~