Ultrafast Electronic Decoherence Dynamics in Molecules

Purdue University, West Lafayette IN

Investigators

Abstract

In this project, the researchers will study the motion of electrons (charge dynamics) inside ionized molecules on time scales of a few femtoseconds (one femtosecond is a millionth of a billionth of a second). Understanding and controlling ultrafast charge dynamics in molecules is of fundamental importance in biochemical processes and the development of molecular scale electronic devices. The research group will use femtosecond laser pulses of various wavelengths to track the motion of the charge and obtain insight into the physical mechanisms that influence it. The results of this project will pave the path towards control of molecular charge dynamics, which is important for the design of laser-controlled chemical reactions and synthesis of quantum materials and devices. To fully realize this potential, a highly trained STEM workforce is essential. As part of this project, a diverse group of graduate and undergraduate students will be trained in ultrafast photon science and quantum science. A detailed understanding of various decoherence/dephasing processes in electronically excited molecules is essential for the development of quantum coherent control protocols for the laser driven control of molecular processes. This is particularly important in molecular ions in which femtosecond and attosecond charge migration dynamics are being intensely studied due to their importance in biochemical processes and charge transport phenomena. When a superposition of multiple ionic states with bandwidth of a few electron volts is created in molecules, electron correlation driven charge migration dynamics can be initiated. Understanding electronic decoherence mechanisms during charge migration is a critical first step towards achieving control of ultrafast charge dynamics in molecules. While multiple previous theoretical and experimental studies have explored charge migration using photoionization probes, nonlinear optical probes of such dynamics can offer a completely novel perspective. Similarly, when molecules are photoionized near shape resonances, the electron temporarily trapped in a shape resonance can affect the evolution of the molecular ion that may be left in a superposition of cationic states. A nonlinear optical measurement can probe the evolution of the molecular ion and shed light on the role played by the shape resonance. In this project, the research group will use nonlinear optical measurements of strong-field and extreme-ultraviolet ionized molecules to obtain direct and detailed information about electronic decoherence dynamics in molecular ions. The objectives are to (1) study electronic decoherence dynamics during strong-field initiated charge migration in molecules such as methyl bromide on few-femtosecond time scales and (2) study the effect of shape resonances on the ultrafast evolution of a molecular ion after XUV photoionization in molecules such as nitrogen and carbon dioxide. 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.