Transcript LGD_RI15_OSU.pptx

Thursday, June 20, 2013 5:44pm
RI15
Absolute VUV photoionization
spectra for HCHO, HO2, and
H2O2 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
1California
Institute of Technology, Pasadena, CA
Research Facility, Sandia National Laboratories, Livermore, CA
3Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA
2Combustion
Introduction
Formaldehyde,
HCHO
IE = 10.88 eV 1
Hydroperoxy radical,
HO2
IE = 11.35 eV 1
Hydrogen peroxide,
H2O2
IE = 10.58 eV 1
• 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
S  E , t     E   N   t 
1Lias,
S.G., "Gas Phase Ion Energetics Data" in NIST Chemistry WebBook, NIST Standard Reference Database
Number 69 Linstrom, P. J.; Mallard, W. G., Eds.
A simple chemical
system yields three
important spectra
Formation and self-reaction of HO2 from Cl2
and CH3OH precursor give HCHO, HO2,
and H2O2.1
Reaction scheme well-constrained =
concentrations predicted with minimal error.
1JPL
Database, Sander, S. P., et al. JPL Publication 10-6 2011.
Sandia Multiplexed
Chemical Kinetics
Reactor
VUV Multiplexed
Photoionization Mass
Spectrometer (MPIMS)1
1Osborn,
D. L., et al. Rev. Sci. Instrum. 2008, 79..
Sandia Multiplexed
Chemical Kinetics
Reactor
VUV Multiplexed
Photoionization Mass
Spectrometer (MPIMS)1
1Osborn,
D. L., et al. Rev. Sci. Instrum. 2008, 79..
Total radical
concentration
Cl atom concentration should be known to high
accuracy for kinetic modeling
37Cl +
2
depletion signal:
1.06 ± 0.02 %
13CH OH+
3
Cl atom concentration:
(1.22 ± 0.07)×1013 molec/cm3
depletion signal:
4.34 ± 0.07 %
Kinetics experiments
to quantify
concentrations
Kinetics model predicts time-dependent concentration based
on well-known rate constants.1,2
S  E , t     E   N   t 
Model convolved with instrument response function.
Typical experimental
conditions:
Photon energy: 11.45 eV
Pressure: 8 Torr
Flow rate: 200 sccm
1Kinetics
2Most
Starting reactants
(molec/cm3):
[CH3OH] = 3.75×1014
[O2] = 7.80×1016
[Cl2] = 8.09×1014
[Cl] = 1.22×1013
model build using Kintecus modeling software. Ianni, J. C. 2002.
rate constants taken from JPL Database, Sander, S. P., et al. JPL Publication 10-6.1.
Formaldehyde absolute
VUV photoionization
spectrum
Compared with absolute cross section measurements
by Cooper, et al.1 and FitzPatrick, et al.2
1Cooper,
G., et al. Chem. Phys. 1996, 209, 61.
B. L., et al. J. Chem. Phys. 2010, 133, 094306..
2FitzPatrick,
HO2 and H2O2 absolute
VUV photoionization
spectra
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.
1Litorja,
M. and Ruscic, B. J. Electron Spectrosc. Relat. Phenom. 1998, 97, 131.
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)