Spatiotemporal reaction kinetics of an ultrafast photoreaction pathway visualized by time-resolved liquid x-ray diffraction
Spatiotemporal reaction kinetics of an ultrafast photoreaction pathway visualized by time-resolved liquid x-ray diffraction
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DOI：
10.1073/pnas.0601958103
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发表时间：
2006-06-20
影响因子：
11.1
通讯作者：
Ihee, Hyotcherl
中科院分区：
文献类型：
--
作者：
Kim, Tae Kyu;Lorenc, Maciej;Ihee, Hyotcherl
用时间分辨X射线衍射法(TRXD)研究了Hgl(2)在甲醇中的反应动力学。尽管大量的时间分辨光谱研究已经提供了关于HGL(2)早期动力学的大量信息，但在从皮秒到微秒的溶液相中缺乏全面的反应机理。在这里，我们展示了TRXD可以直接和定量地提供这种信息。皮秒光脉冲触发了HGL(2)的解离，来自同步加速器的100ps长的x射线脉冲探测了宽时间范围内的演化结构。为了从理论上解释衍射强度，分析中考虑了来自溶质的结构信号、溶质周围的局域结构和整体溶剂的流体动力学。结果表明，溶液中暂态的测定与溶剂能量学密切相关，TRXD可以作为一种超快量热计。它还表明，如果测量足够准确，并应用全局分析，可以同时分辨多种结构通道。通过将我们的模型与实验数据进行一次全局拟合，得到了反应的速率系数，其中包括所有的Q值和时间延迟。所有可能的反应通道的比较证实了二体解离是主要的解离途径。在这个主要的键断裂之后，两个平行的通道继续进行。瞬时Hgl与一个碘原子非优势缔合形成Hgl(2)，I-2是由两个碘原子非双键缔合而成。
We have studied the reaction dynamics for Hgl(2) in methanol by using time-resolved x-ray diffraction (TRXD). Although numerous time-resolved spectroscopic studies have provided ample information about the early dynamics of Hgl(2), a comprehensive reaction mechanism in the solution phase spanning from picoseconds up to microseconds has been lacking. Here we show that TRXD can provide this information directly and quantitatively. Picosecond optical pulses triggered the dissociation of Hgl(2), and 100-ps-long x-ray pulses from a synchrotron probed the evolving structures over a wide temporal range. To theoretically explain the diffracted intensities, the structural signal from the solute, the local structure around the solute, and the hydrodynamics of bulk solvents were considered in the analysis. The results in this work demonstrate that the determination of transient states in solution is strongly correlated with solvent energetics, and TRXD can be used as an ultrafast calorimeter. It also is shown that a manifold of structural channels can be resolved at the same time if the measurements are accurate enough and that global analysis is applied. The rate coefficients for the reactions were obtained by fitting our model against the experimental data in one global fit including all q-values and time delays. The comparison between all putative reaction channels confirms that two-body dissociation is the dominant dissociation pathway. After this primary bond breakage, two parallel channels proceed. Transient Hgl associates nongeminately with an iodine atom to form Hgl(2), and I-2 is formed by nongeminate association of two iodine atoms.