A theoretical study on dissociative photoionization and photoionization cross-sections of a typical ketohydroperoxide in n-butane low-temperature oxidation

Ketohydroperoxides (KHP) are closely relevant to the low-temperature reactivity of hydrocarbons and their derivatives. Photoionization mass spectrometry (PIMS) technology has played a crucial role in de-tecting and quantifying KHP in recent years. However, the dissociative photoionization behavior at the near-threshold may bias the collection of KHP signals, resulting in a significant underestimation of the concentration. In the present study, the dissociative photoionization mechanism of 3-hydroperoxybutanal (3-KHP), the most abundant KHP in n-butane oxidation, was investigated by quantum chemical calcula-tions. The results suggest that a two-step dehydration reaction channel with a low barrier accounts for the observation of fragments at the near-threshold. The appearance energy of possible fragments was obtained at a high theoretical level. The photoionization cross-sections (PICS) of 3-KHP at photon en-ergies ranging from the threshold to 11 eV were obtained by theoretical calculations in this study. By comparing the calculated PICS with the photoionization efficiency curve measured in a previous study, we found that approximately 70% of the 3-KHP signals (m/z = 104) were converted into cation fragments (m/z = 29, 43, 71, etc.) at 10 eV. The theoretically predicted dissociative photoionization fragment infor-mation and total PICS were finally used to refine the quantification of 3-KHP in the previous experiment. Our study indicates that for highly reactive species such as KHP, theoretical investigations on the disso-ciative photoionization behavior and photoionization cross-section will substantially benefit the species quantification by PIMS.(c) 2022 The Combustion Institute. Published by Elsevier Inc. All rights reserved.