Probing the photoisomerization of CHBr3 and CHI3 in solution with transient vibrational and electronic spectroscopy.
Probing the photoisomerization of CHBr3 and CHI3 in solution with transient vibrational and electronic spectroscopy.
复制标题
利用瞬态振动和电子光谱探讨溶液中 CHBr3 和 CHI3 的光致异构化。
DOI：
10.1021/jp310737d
复制
发表时间：
2013
期刊：
影响因子：
--
通讯作者：
F. Crim
中科院分区：
文献类型：
--
作者：
Thomas J. Preston;Michael A. Shaloski;F. Crim
瞬时红外吸收光谱监测30 mM CHBr3和50 mMCHI3在液体CCl4中的凝聚相光解动力学。这些实验具有皮秒的时间分辨率，并监测了母体多卤代甲烷及其光解生成的异构体的C-H伸展区域。这些异构体的C-H伸缩转变在光解iso-CHBr2-BR和iso-CHI2-I后分别出现了约9ps和46pS，其中卤素原子返回形成C-X-X键基序。这些时间尺度与相同样品的瞬时电子吸收光谱的时间演变一致，但又不同，突出了监测振动和电子发色团之间的细微差异。利用振动跃迁跟踪凝聚相反应动力学的特殊性允许重新评估纯CHBr3中光解的瞬时电子光谱，该光谱在400 nm附近具有额外的提示特征。计算表明，这一特征来自于异构体的前体，是新出现的BR片段与附近的CHBr3分子之间的接触对的电荷转移跃迁。稀释度和溶剂研究表明，转变与溶剂无关。然而，根据溶剂的不同，iso-CHBr2-Br2的跃迁波长在400到510 nm的范围内移动。依赖时间的密度泛函计算忠实地再现了这些趋势。
Transient infrared absorption spectroscopy monitors condensed-phase photodissociation dynamics of 30 mM CHBr3 and 50 mM CHI3 in liquid CCl4. The experiments have picosecond time resolution and monitor the C-H stretch region of both the parent polyhalomethanes and their photolytically generated isomers. The C-H stretching transitions of these isomers, in which the emergent halogen atom returns to form a C-X-X bonding motif, appear about 9 ps after photolysis for iso-CHBr2-Br and in about 46 ps for iso-CHI2-I. These time scales are consistent with, but differ from, the time evolution of the transient electronic absorption spectra of the same samples, highlighting the subtle differences between monitoring the vibrational and electronic chromophores. The specificity of using vibrational transitions to track condensed-phase reaction dynamics permits reassessment of the transient electronic spectrum of photolysis in neat CHBr3, which has an additional prompt feature near 400 nm. Calculations show that this feature, which arises from a precursor to the isomer, is a charge-transfer transition of a contact pair between the nascent Br fragment and a nearby CHBr3 molecule. Dilution and solvent studies show that transition is independent of the solvent. The iso-CHBr2-Br transition wavelength, however, shifts over the range of 400 to 510 nm depending on the solvent. Time-dependent density functional calculations faithfully reproduce these trends.