Jet cooled Laser Induced Fluorescence Spectroscopy of FCH2CH2O and other photo-fragments of

XCH2CH2ONO (X=F,Cl,Br,OH)

Rabi Chhantyal-Pun, Ming-Wei Chen, Terry A. Miller

Motivation• OH substituted alkoxy radicals are important intermediate in atmospheric

oxidation of alkenes like Ethene, Butadiene and Isoprene • HOCH2CH2O radical is produced from OH initiated oxidation of Ethene

• Halogen substituted Ethoxy can be a model for the study of HOCH2CH2O radical

Ethene Emission sources

74% Natural sources

26% Human made

Total emission: 18-45 Tg/yr

Ethene sink processes

89% OH

8% O3

3% to the Stratosphere

S. Sawada and T. Totsuka, Atmos. Environ. 20, 821 (1986)

C C

H

H

H

H

OH

C CH

H H

O

H

H

C CH

H

O

H

O

H

H O

O2

C CH

H

O

H

O

H

H

NO

Spectroscopy of Alkoxy radicals

~ ~• Laser Induced Fluorescence (LIF) method has been used in the past to

study the B-X transition of alkoxy radicals• LIF coupled with Supersonic free jet expansion produces rotationally cold

spectrum; rotational contours (obtained even with moderate resolution) can then be used to differentiate different conformers

1-Propoxy

Gapolakrishnan S. PhD thesis The Ohio State University, 2003

XCH2CH2ONO/ He

General Valve ControllerDG535 Pulse Generator

XeF Excimer Laser

Nd:YAG Laser Sirah Dye Laser

Nozzle

T0

PMT

Q-Switch

Flash Lamp

T0 / GPIB

T0

Lens

Frequency Doubler

Precursor preperation: XCH2CH2OH/H2SO4/NaNO2

Experimental apparatus

XCH2CH

2O

NO

LIF survey scan of Photo-Fragments of FCH2CH2ONO

28000 29000 30000 31000 320000

50000

100000

150000

200000

250000

Inte

nsity a

.u.

wavenumber

HCHO

G and T conformers of FEO

Gauche (G) Trans (T)

-Rotational constants were obtained from hf/6-31+g* and ucis/6-31+g*-TDMs were obtained from Ethoxy exp.

0

20

40

60

80

100

120

140

160

Inte

nsity

a.u

.

Sim. T conformer (20K)

30500 30505 30510 30515 30520 30525 30530 30535 305400

20000

40000

60000

80000

100000

120000

140000In

tens

ity a

.u.

wavenumber

Exp.

020406080

100120140160180200

Inte

nsity

a.u

.

Sim. G conformer (20K)

29850 29855 29860 29865 29870 29875 29880 29885 298900

100002000030000400005000060000700008000090000

100000

Inte

nsity

a.u

.

wavenumber

Exp.

Assignment of the Origin bands

28000 29000 30000 31000 320000

50000

100000

150000

200000

250000

Inte

nsity a

.u.

wavenumber

000

000

HCHO

1Gopalakrishnan et. al J. Chem. Phys. 118 (2003) 49–54

Alkoxy Exp.

1-Propoxy G1 28634

1-Propoxt T1 29219

FEO-G 29869

FEO-T 30519

TG

1.531.38

108.2113.6

1.491.51

108.2109.5

104.0111.7

105.3108.4

1.531.38

1.511.52

X and B state geometries

-UCIS/6-31+G(D) HF/6-31+G(D)

76.O 70.0

OCCF dihedral

~ ~

All angles are in degrees and bond lengths are in Å

30000 31000 32000

0

100000

200000

Inte

nsi

ty a

.u.

Wavenumber

00

0

180

117

0

1

180

1170

1

150

1

150

1170

1

150

2

150

2170

1

00

0

140

1

160

1

170

1

140

1170

1

1ucis/6-31+g(d)2Tarcazy et.al. J. Mol. Spec. 220 (2003) 276–29

Mode Exp. Calc.1 Description

17 256 300 Asym CCO/ CCF bend16 513 476 Sym CCO/CCF bend14 699 903 CO stretch18 149 160 CC torsion17 324 358 Sym CCO/CCF bend15 604 832 CO stretch

Conformer Propoxy CO str. FEO Co str.

Exp. 0.76XCalc.2 Exp. 0.79XCalc.2

G 596 590 604 632T 676 642 699 686

ClCH2CH2ONO / FCH2CH2ONO

0

10000

20000

30000

40000

50000

60000

70000

80000

Inte

nsi

ty a

.u.

ClCH2CH

2ONO

27000 27500 28000 28500 29000 29500 30000 30500 31000 31500 320000

30000

60000

90000

120000

150000

180000

210000

240000

Inte

nsi

ty a

.u.

wavenumber

FCH2CH

2ONO

1Gopalakrishnan et. al J. Chem. Phys. 118 (2003) 49–54

HCHO

HCHO

28786?

Alkoxy CO str.

Ethoxy 603Prpoxy-G 596

FEO-G 604 546

Alkoxy Exp.

1-Propoxy G1 28634

1-Propoxt T1 29219

FEO-G 29869FEO-T 30519ClEO-G ClEO-T

-Vinoxy spectrum Brock et. al. JCP 106 10048

28500 29000 29500 30000 305000

10000

20000

30000

40000

50000

60000

70000

80000In

ten

sity a

.u.

ClCH2CH

2ONO

Verification of hot bands

0

10000

20000

30000

40000

50000

60000

70000

80000In

ten

sity

a.u

. Without extension

28400 28600 28800 29000 29200 294000

1000

2000

3000

4000

5000

6000

Inte

nsi

ty a

.u.

wavenumber

With extension

Assignment of Hot bands of Vinoxy

1Brock et. al. JCP 106(24) 10048 1997

28400 28600 28800

10000

20000

30000

40000

50000

60000

70000

Inte

nsity a

.u.

wavenumber

00

0

91

1121

1

91

1121

1

121

192

2122

212

2

291

1

Mode Description X1 B1 X-B Exp.9 CCO bend 500 449 51 51.3

12 CC torsion 404 274 130 127.7

CH2CHO from other XCH2CH2ONO (X=OH,Cl,F,Br)

02000400060008000

10000 FCH2CH

2ONO

0100002000030000

ClCH2CH

2ONO

0

10000

20000

30000 BrCH

2CH

2ONO

28400 28500 28600 28700 288000

2000400060008000

10000

Inte

nsity

a.u

.

wavenumber

HOCH2CH

2ONO

Conclusion

• Obtained and analyzed the Laser Induced Fluorescence spectrum of B-X transition of FEO radical

• CH2CHO and HCHO fragments are produced following the photodissociation of XCH2CH2ONO (X= OH, F, Cl, Br)

• Analysis of the mechanism for the formation of CH2CHO is going on

~ ~

Acknowledgement

• Professor Terry Miller (advisor)• Miller group members Dr. Dmitry Melnik Dr. Jin Jun Liu Neal Kline Terrance Codd

• DOE for funding

Possible mechanism

351 nm

C

C

O

NO

H

H

H-HCl

C C

H

H

H

O

NO

C C O

N

O

Cl

H

H H

H

C C OCl

H

H H

H

N O

C C

H

H

H

O

C

H

H

ClC

O

H H

351 nm

-HCl