TORSIONAL EXCITATION IN O-H STRETCH OVERTONE SPECTRA OF ETHYL HYDROPEROXIDE CONFORMERS

Shizuka Hsieh, Ma Thida, Margaret Nyamumbo, Hannah Hitchner, Noah Naamad, Kelly Smith, Robert G. Linck

Department of Chemistry, Smith College, Northampton, MA 01063

Atmospheric hydroperoxide formation

Reeves and Penkett. Chem. Rev. 103, 5199 (2003)Lee et al. Atmos. Environ. 34, 34775 (2000)

High NO Low NO

Aldehyde

OH radicals from O-H stretch overtone excitation

Closser, Vogelhuber and Hsieh. J. Phys. Chem. A 112, 1238 (2008)

LIF

sign

al

lOvertone

635 625 615 605 595

(nm)LIF

CH3CH2OOH

CH3CH2O + OH

1

2

3

4

5

6

O-H stretch overtone excitation for 3-6 quanta

Homitsky et al. J. Phys. Chem. A 108, 9492 (2004)

CH3CH2OOH

1

2

3

4

5

6

Photoacoustic spectra for 3-6 quanta of O-H stretch

Wavenumbers (cm-1)

s (1

0-22 cm

2 mol

ecul

e-1)

s (1

0-23 cm

2 mol

ecul

e-1)

s (1

0-24 cm

2 mol

ecul

e-1)

3nOH 4nOH 5nOH 6nOH

Photoacoustic spectra for 3-6 quanta of O-H stretch

Wavenumbers (cm-1)

s (1

0-22 cm

2 mol

ecul

e-1)

s (1

0-23 cm

2 mol

ecul

e-1)

s (1

0-24 cm

2 mol

ecul

e-1)

3nOH 4nOH 5nOH 6nOH

** * *

**

Potentials for O-O torsion

Wavenumbers (cm-1)

s (1

0-22 cm

2 mol

ecul

e-1)

s (1

0-23 cm

2 mol

ecul

e-1)

s (1

0-24 cm

2 mol

ecul

e-1)

Dihedral angle180 180 180 180

Ener

gy (c

m-1

)

3nOH

4nOH

5nOH

6nOH

Potentials for O-O torsion

Wavenumbers (cm-1)

s (1

0-22 cm

2 mol

ecul

e-1)

s (1

0-23 cm

2 mol

ecul

e-1)

s (1

0-24 cm

2 mol

ecul

e-1)

Dihedral angle180 180 180 180

Ener

gy (c

m-1

)

3nOH

4nOH

5nOH

6nOH

Simulated absorption spectra (preliminary)

Wavenumbers (cm-1)

s (1

0-22 cm

2 mol

ecul

e-1)

s (1

0-23 cm

2 mol

ecul

e-1)

s (1

0-24 cm

2 mol

ecul

e-1)

3nOH 4nOH 5nOH 6nOH

Simulated absorption spectra (preliminary)

Wavenumbers (cm-1)

s (1

0-22 cm

2 mol

ecul

e-1)

s (1

0-23 cm

2 mol

ecul

e-1)

s (1

0-24 cm

2 mol

ecul

e-1)

3nOH 4nOH 5nOH 6nOH

Conformer population

O-H stretch overtone excitation for 3-6 quanta

Wavenumbers (cm-1)

s (1

0-22 cm

2 mol

ecul

e-1)

s (1

0-23 cm

2 mol

ecul

e-1)

s (1

0-24 cm

2 mol

ecul

e-1)

3nOH 4nOH 5nOH 6nOH

** * *

**

Acknowledgements

Katy Meek Ma Thida Lauren Owen Margaret Nyamumbo

Camille & Henry Dreyfus FoundationNational Science Foundation

Smith College

Calculated O-H stretch frequencies

Calculated dissociation energy

Hou et al. J. Phys. Chem. 109, 112 (2005)

Calculated D0 = 41.6 kcal mol-1

OH radicals from O-H stretch overtone excitation

4nOH

6nOH

5nOH

Wavelength (nm)

Figure adapted from Matthews, Sinha and Francisco, PNAS 102, 7449 (2005)