Center for Time-Resolved Diffraction, Department of Chemistry, KAIST, Daejeon 305-701, Republic of Korea.
J Am Chem Soc. 2013 Feb 27;135(8):3255-61. doi: 10.1021/ja312513w. Epub 2013 Feb 15.
Molecules are often born with high energy and large-amplitude vibrations. In solution, a newly formed molecule cools down by transferring energy to the surrounding solvent molecules. The progression of the molecular and solute-solvent cage structure during this fundamental process has been elusive, and spectroscopic data generally do not provide such structural information. Here, we use picosecond X-ray liquidography (solution scattering) to visualize time-dependent structural changes associated with the vibrational relaxation of I(2) molecules in two different solvents, CCl(4) and cyclohexane. The birth and vibrational relaxation of I(2) molecules and the associated rearrangement of solvent molecules are mapped out in the form of a temporally varying interatomic distance distribution. The I-I distance increases up to ~4 Å and returns to the equilibrium distance (2.67 Å) in the ground state, and the first solvation cage expands by ~1.5 Å along the I-I axis and then shrinks back accompanying the structural change of the I(2) molecule.
分子通常具有较高的能量和大振幅振动。在溶液中，新形成的分子通过将能量传递给周围的溶剂分子来冷却。在这个基本过程中，分子和溶质-溶剂笼结构的演变一直难以捉摸，光谱数据通常无法提供这种结构信息。在这里，我们使用皮秒 X 射线液体学（溶液散射）来可视化与 I(2)分子在两种不同溶剂（四氯化碳和环己烷）中的振动弛豫相关的随时间变化的结构变化。I(2)分子的生成和振动弛豫以及溶剂分子的相关重排以随时间变化的原子间距离分布的形式绘制出来。I-I 距离增加到约 4 Å 并回到基态的平衡距离（2.67 Å），第一个溶剂笼沿 I-I 轴扩展约 1.5 Å，然后随着 I(2)分子的结构变化收缩回去。
