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首页> 外文期刊>The journal of physical chemistry, A. Molecules, spectroscopy, kinetics, environment, & general theory >Broadband spectral probing revealing ultrafast photochemical branching after ultraviolet excitation of the aqueous phenolate anion
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Broadband spectral probing revealing ultrafast photochemical branching after ultraviolet excitation of the aqueous phenolate anion

机译：宽带光谱探测揭示了紫外激发酚酸根阴离子后的超快速光化学分支

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摘要

Electron photodetachment from the aromatic anion phenolate excited into the π - π* singlet excited state (S_1) in aqueous solution is studied with ultrafast transient absorption spectroscopy with a time resolution of better than 50 fs. Broad-band transient absorption spectra from 300 to 690 nm are recorded. The transient bands are assigned to the solvated electron, the phenoxyl radical, and the phenolate S_1 excited state, and confirmation of these assignments is achieved using both KNO_3 as electron quencher and time-resolved fluorescence to measure singlet excited state dynamics. The phenolate fluorescence lifetime is found to be short (?20 ps) in water, but the fast decay is only in part due to the electron ejection channel from S_1. Using global target analysis, two electron ejection channels are identified, and we propose that both vibrationally hot S_1 state and the relaxed S_1 state are direct precursors for the solvated electron. Therefore, electron ejection is found just to compete with picosecond time scale vibrational relaxation and electronic radiationless decay channels. This contrasts markedly with <100 fs electron detachment processes for inorganic anions.
机译：用超快瞬态吸收光谱法研究了在水溶液中被激发成π-π*单重态激发态（S_1）的芳族阴离子酚盐的电子光解离，其时间分辨率优于50 fs。记录了300至690 nm的宽带瞬态吸收光谱。将瞬态谱带分配给溶剂化电子，苯氧基和酚盐S_1激发态，并使用KNO_3作为电子猝灭剂和时间分辨荧光来测量单重激发态动力学，从而实现对这些分配的确认。发现水中的酚盐荧光寿命短（约20 ps），但快速衰减仅部分归因于来自S_1的电子喷射通道。使用全局目标分析，确定了两个电子喷射通道，我们建议振动热的S_1状态和弛豫的S_1状态都是溶剂化电子的直接前驱体。因此，发现电子喷射正好与皮秒级的时标振动弛豫和电子无辐射衰减通道竞争。这与无机阴离子的<100 fs电子离解过程形成鲜明对比。

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