1. 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

2. Atmospheric hydroperoxide formation Reeves and Penkett. Chem. Rev. 103, 5199 (2003) Lee et al. Atmos. Environ. 34, 34775 (2000) High NOLow NO Aldehyde

3. OH radicals from O-H stretch overtone excitation Closser, Vogelhuber and Hsieh. J. Phys. Chem. A 112, 1238 (2008) LIF signal Overtone 635 625 615 605 595 (nm) LIF CH 3 CH 2 OOH CH 3 CH 2 O + OH 1 2 3 4 5 6

4. O-H stretch overtone excitation for 3-6 quanta Homitsky et al. J. Phys. Chem. A 108, 9492 (2004) CH 3 CH 2 OOH 1 2 3 4 5 6

5. Photoacoustic spectra for 3-6 quanta of O-H stretch Wavenumbers (cm -1 )  (10 -22 cm 2 molecule -1 )  (10 -23 cm 2 molecule -1 )  (10 -24 cm 2 molecule -1 ) 3 OH 4 OH 5 OH 6 OH

6. Photoacoustic spectra for 3-6 quanta of O-H stretch Wavenumbers (cm -1 )  (10 -22 cm 2 molecule -1 )  (10 -23 cm 2 molecule -1 )  (10 -24 cm 2 molecule -1 ) 3 OH 4 OH 5 OH 6 OH * * * * * *

7. Potentials for O-O torsion Wavenumbers (cm -1 )  (10 -22 cm 2 molecule -1 )  (10 -23 cm 2 molecule -1 )  (10 -24 cm 2 molecule -1 ) Dihedral angle 180 Energy (cm -1 ) 3 OH 4 OH 5 OH 6 OH

8. Potentials for O-O torsion Wavenumbers (cm -1 )  (10 -22 cm 2 molecule -1 )  (10 -23 cm 2 molecule -1 )  (10 -24 cm 2 molecule -1 ) Dihedral angle 180 Energy (cm -1 ) 3 OH 4 OH 5 OH 6 OH

9. Simulated absorption spectra (preliminary) Wavenumbers (cm -1 )  (10 -22 cm 2 molecule -1 )  (10 -23 cm 2 molecule -1 )  (10 -24 cm 2 molecule -1 ) 3 OH 4 OH 5 OH 6 OH

10. Simulated absorption spectra (preliminary) Wavenumbers (cm -1 )  (10 -22 cm 2 molecule -1 )  (10 -23 cm 2 molecule -1 )  (10 -24 cm 2 molecule -1 ) 3 OH 4 OH 5 OH 6 OH Conformer population

11. O-H stretch overtone excitation for 3-6 quanta Wavenumbers (cm -1 )  (10 -22 cm 2 molecule -1 )  (10 -23 cm 2 molecule -1 )  (10 -24 cm 2 molecule -1 ) 3 OH 4 OH 5 OH 6 OH * * * * * *

12. Acknowledgements Katy Meek Ma Thida Lauren Owen Margaret Nyamumbo Camille & Henry Dreyfus Foundation National Science Foundation Smith College

13. Calculated O-H stretch frequencies

14. Calculated dissociation energy Hou et al. J. Phys. Chem. 109, 112 (2005) Calculated D 0 = 41.6 kcal mol -1

15. OH radicals from O-H stretch overtone excitation 4 OH 6 OH 5 OH Wavelength (nm) Figure adapted from Matthews, Sinha and Francisco, PNAS 102, 7449 (2005)