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Published February 26, 2015 | Supplemental Material
Journal Article Open

VUV Photoionization Cross Sections of HO₂, H₂O₂, and H₂CO


The absolute vacuum ultraviolet (VUV) photoionization spectra of the hydroperoxyl radical (HO₂), hydrogen peroxide (H₂O₂), and formaldehyde (H_2CO) have been measured from their first ionization thresholds to 12.008 eV. HO₂, H₂O₂, and H₂CO were generated from the oxidation of methanol initiated by pulsed-laser-photolysis of Cl₂ in a low-pressure slow flow reactor. Reactants, intermediates, and products were detected by time-resolved multiplexed synchrotron photoionization mass spectrometry. Absolute concentrations were obtained from the time-dependent photoion signals by modeling the kinetics of the methanol oxidation chemistry. Photoionization cross sections were determined at several photon energies relative to the cross section of methanol, which was in turn determined relative to that of propene. These measurements were used to place relative photoionization spectra of HO₂, H₂O₂, and H₂CO on an absolute scale, resulting in absolute photoionization spectra.

Additional Information

© 2015 American Chemical Society. Received: September 4, 2014. Revised: January 22, 2015. Publication Date (Web): January 26, 2015. Acknowledgment The Caltech effort was supported by the National Science Foundation grants CHE-0957490 and CHE-1413712 and the National Aeronautics and Space Administration's (NASA) Upper Atmospheric Research Program grant NNX12AI01G. L.G.D. was supported by an EPA STAR Fellowship and a Sandia Campus Executive Fellowship. N.C.E. was supported in part by a Dreyfus Foundation Postdoctoral Fellowship in Environmental Chemistry. Part of this research was carried out by the Jet Propulsion Laboratory, California Institute of Technology, under contract with NASA. The participation of D.L.O., J.D.S., O.W., and C.A.T. and the development and maintenance of the MPIMS apparatus are supported by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences. Sandia is a multiprogram laboratory operated by Sandia Corporation, a Lockheed Martin Company, for the National Nuclear Security Administration under contract DE-AC04-94-AL85000. The research conducted used resources of the Advanced Light Source, which is a DOE Office of Science User Facility at Lawrence Berkeley National Laboratory under contract DE-AC02-05CH11231. The authors declare no competing financial interest.

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