Multidimensional Femtosecond Studies of Chemical Reaction Dynamics

该项目由化学部的化学结构、动力学和机理(CSDM-A)计划资助。科罗拉多大学博尔德分校的大卫·乔纳斯教授正在开发飞秒激光技术来研究电子在分子中的运动。飞秒是十亿分之一秒的百万分之一秒。在分子内部，原子和慢电子在飞秒时间尺度上运动。该项目的目标是测量当推动原子和电子运动的力很弱时，原子和电子运动是如何联系在一起的。这种弱力可以从热能量级的能量中产生。这个项目探索驱动电子运动所需的最小能量。类似的电子运动也涉及到照明、显示和光合作用。三维光谱将电子运动和原子运动联系起来。高对称性分子简化了电子和原子运动的研究。在3D傅里叶变换光谱学中，四波混频被用来记录脉冲之间三个时间延迟的瞬时信号。关于三个时间延迟的三重傅立叶变换生成作为三个频率轴的函数的频谱。与大多数2D频谱不同，脉冲频谱和脉冲传播效应可以在3D中分开。这揭示了潜在的3D非线性响应，它应该独立于实验条件。来自透明溶剂中的交叉相位调制的信号产生紧凑的时间域瞬变，用于基本3D响应的初始实验恢复。具有伪Jahn-Teller效应的高对称性分子的2D和3D电子能谱可以通过与量子力学计算的比较来揭示其飞秒电子布居转移的机制。这些计算充分考虑了电子运动和原子振动之间的非绝热相互作用。该项目的更广泛的影响包括对学生进行现代实验和计算技术的培训，以及更好地了解驱动电子运动所需的最低能量所带来的潜在社会好处。该奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

This project is funded by the Chemical Structure, Dynamics and Mechanism (CSDM-A) program of the Chemistry Division. Professor David Jonas of the University of Colorado at Boulder is developing femtosecond laser techniques to study the motion of electrons in molecules. A femtosecond is a millionth of a billionth of a second. Inside molecules, atoms and slow electrons move on the femtosecond timescale. The goal of the project is to measure how atomic and electronic motions are linked when the forces driving their motion are weak. Such weak forces can arise from energies on the order of the thermal energy. This project explores the smallest energy required to drive motion of electrons. Similar electronic motions are involved in lighting, displays, and photosynthesis. Three dimensional spectra correlate electronic and atomic motion. High symmetry molecules simplify the study of electronic and atomic motions.In 3D Fourier transform spectroscopy, four-wave mixing is used to record transient signals as a function of three time delays between pulses. Triple Fourier transformation with respect to the three time delays generates a spectrum that is a function of three frequency axes. Unlike most 2D spectra, the pulse spectra and pulse propagation effects can be divided out in 3D. This reveals the underlying 3D nonlinear response, which should be independent of experimental conditions. The signal from cross-phase modulation in transparent solvents produces compact time-domain transients for initial experimental recovery of the underlying 3D response. 2D and 3D electronic spectroscopy of high symmetry molecules with pseudo Jahn-Teller effects can reveal the mechanism of their femtosecond electronic population transfer through comparison to quantum mechanical calculations. The calculations fully incorporate non-adiabatic interactions between motion of electrons and the vibrational motion of atoms. The broader impacts of this project include training of students in modern experimental and computational techniques plus potential societal benefits from a better understanding of the minimum energy required to drive electronic motion.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.