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首页> 外文期刊>The journal of physical chemistry, A. Molecules, spectroscopy, kinetics, environment, & general theory >Quantum Chemical Characterization of Low-Lying Excited States of an Aryl Peroxycarbonate: Mechanistic Implications for Photodissociation
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Quantum Chemical Characterization of Low-Lying Excited States of an Aryl Peroxycarbonate: Mechanistic Implications for Photodissociation

机译：过酸碳酸芳基酯低激发态的量子化学表征：光解离的机械意义

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摘要

Recent experiments have revealed the existence of an excited state dissociative mechanism for certain peroxycarbonates, with the demonstration that the lifetime of the excited state matches the picosecond time scale for appearance of nascent carbon dioxide product. The data infer that the photoreaction proceeds via an effectively concerted three-body dissociation within the lifetime of the singlet excited state. Many other arylperoxides decay sequentially via [(aryloxy)carbonyl]oxy radical intermediates on nanosecond-microsecond time scales. Uncertainty as to the lifetime of the excited state relates to the character and the relative energetic ordering of states of the parent molecule, since the spectra and photochemistry imply that low-lying states may exist on each of the aryl, carbonate, and peroxide chemical functionalities. We employ many-body electronic structure calculations to determine the energies and characters of the low-lying valence states of a minimal aryl peroxycarbonate model germane to the above-mentioned experiments, methyl phenyl peroxycarbonate (MPC). Our results indicate that the lowest-lying state is an intrinsically nondissociative aryl ππ* excited state. We identify additional low-lying states that are expected to be dissociative in nature and propose that the time scales observed for the dissociation reaction may correspond to the time scale for transfer of excited state population to these states.
机译：最近的实验已经揭示了某些过氧碳酸盐存在激发态解离机制，并证明了激发态的寿命与新生二氧化碳产物出现的皮秒时间尺度相匹配。数据推断光反应是在单重态激发态的寿命内通过有效协调的三体解离而进行的。许多其他的芳基过氧化物通过[（芳氧基）羰基]氧基自由基中间体在纳秒-微秒的时间尺度上依次衰减。激发态寿命的不确定性与母体分子的特征和状态的相对能级有关，因为光谱和光化学表明低价态可能存在于芳基，碳酸酯和过氧化物的化学官能团上。我们采用多体电子结构计算方法来确定与上述实验紧密相关的最小芳基过氧碳酸酯模型（MPC）的能量和低价态的特征。我们的结果表明，最低处的状态是本质上非解离的芳基ππ*激发态。我们确定了有望在本质上解离的其他低洼状态，并建议为解离反应观察到的时间尺度可能与将激发态种群转移到这些状态的时间尺度相对应。

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