Observation of ultrafast chemical dynamics using femtosecond laser spectroscopy

许多重要的光化学反应发生在飞秒到皮秒的时间尺度上，需要使用超快激光光谱方法来观察化学动力学。该项目将使用飞秒激光脉冲来启动和监测分离的气相分子和溶液中的光化学变化过程，使人们能够精确地了解分子动力学是如何被周围的溶剂改变的。气相实验将使用速度图成像和超快库仑爆炸方法来拍摄光激发分子的演变结构的快照，从而跟踪在带电的分子中化学键断裂时发生的变形。溶液相研究将使用红外、可见光和紫外区的瞬时吸收光谱来观察光激发分子经历的电子态的变化，它们与周围溶剂的相互作用，多余能量的耗散到溶剂浴，以及与其他溶质分子的反应。这些补充研究的结果将是分子在吸收紫外线后异构化、解离或松弛步骤的时间常数和速率系数。实验研究将利用布里斯托尔实验室由EPSRC支持的两个实验：由EP/L005913/1资助的库仑爆炸和速度图成像实验，以及由EP/R012695/1支持的超快瞬时吸收光谱实验。

Many important photochemical reactions occur on timescales from femtosecond to picosecond, requiring the use of ultrafast laser spectroscopy methods to observe the chemical dynamics. This project will use femtosecond laser pulses to initiate and monitor processes of photochemical change, both in isolated gas-phase molecules and in solution, allowing the development of a precise understanding of how the molecular dynamics are modified by a surrounding solvent. The gas-phase experiments will use velocity map imaging and ultrafast Coulomb explosion methods to take snapshots of the evolving structures of photoexcited molecules, thereby tracking the deformations which occur as chemical bonds are broken in energized molecules. The solution phase studies will use transient absorption spectroscopy in the infra-red, visible and ultraviolet regions to observe the changes in electronic state which photoexcited molecules undergo, their interactions with the surrounding solvent, dissipation of excess energy to the solvent bath, and reactions with other solute molecules. The outcomes of these complementary studies will be time constants and rate coefficients for the steps in molecular isomerization, dissociation or relaxation following absorption of ultraviolet radiation.The experimental studies will make use of two EPSRC-supported experiments in the Bristol laboratory: a Coulomb explosion and velocity map imaging experiment funded by EP/L005913/1 and an ultrafast transient absorption spectroscopy experiment supported by EP/R012695/1.