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    VUV Photoionization Cross Sections of HO<sub>2</sub>, H<sub>2</sub>O<sub>2</sub>, and H<sub>2</sub>CO

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    The absolute vacuum ultraviolet (VUV) photoionization spectra of the hydroperoxyl radical (HO<sub>2</sub>), hydrogen peroxide (H<sub>2</sub>O<sub>2</sub>), and formaldehyde (H<sub>2</sub>CO) have been measured from their first ionization thresholds to 12.008 eV. HO<sub>2</sub>, H<sub>2</sub>O<sub>2</sub>, and H<sub>2</sub>CO were generated from the oxidation of methanol initiated by pulsed-laser-photolysis of Cl<sub>2</sub> 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 HO<sub>2</sub>, H<sub>2</sub>O<sub>2</sub>, and H<sub>2</sub>CO on an absolute scale, resulting in absolute photoionization spectra
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