We investigated the simplest alkylperoxy radical, CH₃OO, formed by reacting photolytically generated CH₃ radicals with O₂, using the new combustion reactions followed by photoelectron photoion coincidence (CRF-PEPICO) apparatus at the Swiss Light Source. Modeling the experimental photoion mass-selected threshold photoelectron spectrum using Franck–Condon simulations including transitions to triplet and singlet cationic states yielded the adiabatic ionization energy of 10.265 ± 0.025 eV. Dissociative photoionization of CH₃OO generates the CH₃⁺ fragment ion at the appearance energy of 11.164 ± 0.010 eV. Combining these two values with Δ_fH_0K^°(CH₃) yields Δ_fH_0K^°(CH₃OO) = 22.06 ± 0.97 kJ mol^–1, reducing the uncertainty of the previously determined value by a factor of 5. Statistical simulation of the CH₃OO breakdown diagram provides a molecular thermometer of the free radical’s internal temperature, which we measured to be 330 ± 30 K.

中文翻译：

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自由基温度计，热化学和光电子能谱：甲基过氧自由基的光电子光子符合光谱研究

我们研究了最简单的烷基过氧自由基CH ₃ OO，该自由基是通过在瑞士光源处使用新的燃烧反应以及随后的光电子光子重合（CRF-PEPICO）装置使光解生成的CH ₃自由基与O ₂反应而形成的。使用Franck–Condon模拟（包括向三重态和单重态阳离子态的跃迁）对实验光离子质量选择的阈值光电子光谱进行建模，可产生绝热电离能，为10.265±0.025 eV。CH ₃ OO的解离光电离可在11.164±0.010 eV的出现能下生成CH ₃ ⁺碎片离子。将这两个值与_Δf H _0K ^°组合（CH ₃）得到Δ _˚F ħ _0K ^°（CH ₃ OO）= 22.06±0.97千焦耳摩尔^-1，由5. CH统计模拟的因子减少先前确定的值的不确定性₃ OO击穿图提供一个分子自由基内部温度的温度计，我们测得为330±30K。