Non-Adiabatic Dynamics in Molecules Driven by Strong Laser Fields

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Professor Weinacht and his research team of graduate and undergraduate students will develop and use ultrafast-pulse high-power lasers to study the motion of electrons and nuclei in molecules. Observing such motion will advance our understanding of many natural processes in which the electrons and nucleus act in concert, including vision, energy storage, energy conversion, and chemical transformation. Understanding these dynamics is also important for the development of new technologies such as solar cells, ultrafast molecular switches, and quantum computers. While lasers are natural tools for manipulating and measuring electrons in molecules, one requires very short laser pulses in order to manipulate electrons in real time. The investigators in this project will use intense ultrashort laser pulses (with intensities far greater than at the surface of the sun, and durations of less than a hundredth of a trillionth of a second!) in order to ionize molecules, removing one of the many electrons bound to the molecule. They will take pictures of the electrons as they come off the molecules, making use of a technique called 'velocity map imaging'. These pictures can be used to understand the coupled dynamics of electrons and nuclei during ionization, which is important for understanding chemical dynamics and for developing high speed electronics.The experimental work will develop pulse shape spectroscopy in order to follow nonadiabatic dynamics in molecules. The work will compare measurements of strong field molecular ionization using shaped ultrafast laser pulses with more traditional pump probe measurements of excited state dynamics. The two approaches contain complementary information on coupled electron nuclear dynamics, which can be uncovered via detailed comparisons with calculations of the measurement observables. The work will deepen our understanding of nonadiabatic dynamics in molecules. Recent measurements from the group have highlighted the ability to control internal conversion with shaped laser pulses. This allowed the group to follow the evolution of electronic coherence through internal conversion and measure the coherence time for a series of halogenated methane molecules. The group will extend these measurements to a new family of organic ring molecules, pyrrole, furan and thiophene, and compare the measurements with time resolved photoelectron spectroscopy measurements made in the group's laboratory. This will allow the group to develop pulse shape spectroscopy as a powerful tool for following electronic and nuclear dynamics with a rigorous interpretation based on comparison with theory and complementary experiments.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.