Photoexcitation of iodide ion-pyrimidine clusters above the electron detachment threshold: Intracluster electron transfer versus nucleobase-centred excitations
Photoexcitation of iodide ion-pyrimidine clusters above the electron detachment threshold: Intracluster electron transfer versus nucleobase-centred excitations
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DOI：
10.1063/1.5018168
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发表时间：
2018-02-28
影响因子：
4.4
通讯作者：
Dessent, Caroline E. H.
中科院分区：
文献类型：
--
作者：
Matthews, Edward;Cercola, Rosaria;Dessent, Caroline E. H.
本文首次对胸腺嘧啶和胞嘧啶碱基团簇进行了电子解离阈值以上的激光光解离光谱研究，探讨了激发态和光解离通道。虽然光耗尽是强的，只有微弱的离子光碎片信号观察到，表明集群衰减主要是由电子脱离。I-中心点T和I-中心点C团簇的光耗尽光谱在垂直脱离能附近（类似于4.0 eV）显示出突出的偶极束缚激发态（I）。与先前研究的I-中心点尿嘧啶（I-center dot U）簇[W. L. Li等人，J. Chem.Phys.145，044319（2016）]，I-中心点T簇也显示出中心在4.8eV的第二激发态（II），我们类似地将其分配给pi-pi* 核碱基局部跃迁。然而，在I中心点C的光谱中没有明显的高能量吸收带。含时密度泛函理论（TDDFT）计算表明，虽然I-中心点T和I-中心点U团簇中的每一个都显示出一个单一的主要π-π * 核碱基局域跃迁，但I-中心点C的相应π-π * 核碱基跃迁被分成三个单独的较弱的电子激发。I-和去质子化的核碱基阴离子的光片段后，观察到的I-中心点U和I-中心点T的光激发，与行动光谱显示带（在4.0和4.8 eV）的I-和去质子化的核碱基阴离子的生产。的I-中心点C集群的光致碎裂行为是独特的，因为它的I（-）photorfragment显示一个相对平坦的配置文件以上预期的垂直脱离能量。我们讨论了所观察到的光致碎裂配置文件的I-中心点嘧啶集群，在以前的时间分辨测量的背景下，并得出结论，所观察到的光激发主要是一致的簇内电子转移占主导地位的近阈值区域，而核碱基为中心的激发占主导地位接近4.8 eV。TDDFT计算表明电荷转移跃迁[Iodide n（5 p（6））-> Uracil sigma*]可能对整个扫描光谱区域的团簇吸收分布有贡献，并讨论了这些态的可能作用。出版社：AIP Publishing
Laser photodissociation spectroscopy of the I-center dot thymine (I-center dot T) and I-center dot cytosine (I-center dot C) nucleobase clusters has been conducted for the first time across the regions above the electron detachment thresholds to explore the excited states and photodissociation channels. Although photodepletion is strong, only weak ionic photofragment signals are observed, indicating that the clusters decay predominantly by electron detachment. The photodepletion spectra of the I-center dot T and I-center dot C clusters display a prominent dipole-bound excited state (I) in the vicinity of the vertical detachment energy(similar to 4.0 eV). Like the previously studied I-center dot uracil (I-center dot U) cluster [W. L. Li et al., J. Chem. Phys. 145, 044319 (2016)], the I-center dot T cluster also displays a second excited state (II) centred at 4.8 eV, which we similarly assign to a pi-pi* nucleobase-localized transition. However, no distinct higher-energy absorption bands are evident in the spectra of the I-center dot C. Time-dependent density functional theory (TDDFT) calculations are presented, showing that while each of the I-center dot T and I-center dot U clusters displays a single dominant pi-pi* nucleobase-localized transition, the corresponding pi-pi* nucleobase transitions for I-center dot C are split across three separate weaker electronic excitations. I- and deprotonated nucleobase anion photofragments are observed upon photoexcitation of both I-center dot U and I-center dot T, with the action spectra showing bands (at 4.0 and 4.8 eV) for both the I- and deprotonated nucleobase anion production. The photofragmentation behaviour of the I-center dot C cluster is distinctive as its I(-)photofragment displays a relatively flat profile above the expected vertical detachment energy. We discuss the observed photofragmentation profiles of the I-center dot pyrimidine clusters, in the context of the previous time-resolved measurements, and conclude that the observed photoexcitations are primarily consistent with intracluster electron transfer dominating in the near-threshold region, while nucleobase-centred excitations dominate close to 4.8 eV. TDDFT calculations suggest that charge-transfer transitions [Iodide n (5p(6)) -> Uracil sigma*] may contribute to the cluster absorption profile across the scanned spectral region, and the possible role of these states is also discussed. Published by AIP Publishing.