1. Absolute VUV photoionization spectra for HCHO, HO 2, and H 2 O 2 from 10.5-11.5 eV Leah G. Dodson, 1 Linhan Shen, 1 John D. Savee, 2 Nathan C. Eddingsaas, 1 Oliver Welz, 2 Craig A. Taatjes, 2 David L. Osborn, 2 Stanley P. Sander, 3 and Mitchio Okumura, 1 1 California Institute of Technology, Pasadena, CA 2 Combustion Research Facility, Sandia National Laboratories, Livermore, CA 3 Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA Thursday, June 20, 2013 5:44pm RI15

2. Introduction Absolute VUV photoionization spectra difficult to obtain for these three species Need accurate number density ([N](t)) to obtain absolute cross section (σ(E)) We use a chemical kinetics model to determine concentrations with low error Formaldehyde, HCHO IE = 10.88 eV 1 Hydroperoxy radical, HO 2 IE = 11.35 eV 1 Hydrogen peroxide, H 2 O 2 IE = 10.58 eV 1 1 Lias, S.G., "Gas Phase Ion Energetics Data" in NIST Chemistry WebBook, NIST Standard Reference Database Number 69 Linstrom, P. J.; Mallard, W. G., Eds.

3. A simple chemical system yields three important spectra Formation and self-reaction of HO 2 from Cl 2 and CH 3 OH precursor give HCHO, HO 2, and H 2 O 2. 1 Reaction scheme well-constrained = concentrations predicted with minimal error. 1 JPL Database, Sander, S. P., et al. JPL Publication 10-6 2011.

4. Sandia Multiplexed Chemical Kinetics Reactor VUV Multiplexed Photoionization Mass Spectrometer (MPIMS) 1 1 Osborn, D. L., et al. Rev. Sci. Instrum. 2008, 79..

5. Sandia Multiplexed Chemical Kinetics Reactor VUV Multiplexed Photoionization Mass Spectrometer (MPIMS) 1 1 Osborn, D. L., et al. Rev. Sci. Instrum. 2008, 79..

6. Total radical concentration 37 Cl 2 + depletion signal: 1.06 ± 0.02 % Cl atom concentration should be known to high accuracy for kinetic modeling 13 CH 3 OH + depletion signal: 4.34 ± 0.07 % Cl atom concentration: (1.22 ± 0.07)×10 13 molec/cm 3

7. Kinetics experiments to quantify concentrations Kinetics model predicts time-dependent concentration based on well-known rate constants. 1,2 Model convolved with instrument response function. 1 Kinetics model build using Kintecus modeling software. Ianni, J. C. 2002. 2 Most rate constants taken from JPL Database, Sander, S. P., et al. JPL Publication 10-6.1. Typical experimental conditions: Photon energy: 11.45 eV Pressure: 8 Torr Flow rate: 200 sccm Starting reactants (molec/cm 3 ): [CH 3 OH] = 3.75×10 14 [O 2 ] = 7.80×10 16 [Cl 2 ] = 8.09×10 14 [Cl] = 1.22×10 13

8. Formaldehyde absolute VUV photoionization spectrum 1 Cooper, G., et al. Chem. Phys. 1996, 209, 61. 2 FitzPatrick, B. L., et al. J. Chem. Phys. 2010, 133, 094306.. Compared with absolute cross section measurements by Cooper, et al. 1 and FitzPatrick, et al. 2

9. HO 2 and H 2 O 2 absolute VUV photoionization spectra 1 Litorja, M. and Ruscic, B. J. Electron Spectrosc. Relat. Phenom. 1998, 97, 131. Compared with relative cross section measurements by Litorja and Ruscic. 1 Results from Litorja and Ruscic were scaled to the absolute spectra measured here for qualitative shape agreement. Residual methanol

10. Acknowledgements: Caltech: Linhan Shen, Nathan Eddingsaas (RIT), Kana Takematsu, Aaron Noell, Mitchio Okumura, Stan Sander (JPL), Fred Grieman (Pomona) Sandia: John Savee, Oliver Welz, Craig Taatjes, David Osborn LBNL: Stephen Leone, Musa Ahmed, Kevin Wilson Funding: EPA STAR Fellowship (LGD) NSF, NASA, DOE, Dreyfus (NCE)