Closing the Loop on Bond Selective Chemistry Using Tailored Strong Field Laser Pulses

Abstract

Strong field, closed-loop control of gas-phase photochemical reactivity is the focus of this article. The control of chemical reactivity is now possible using tailored laser pulses to circumvent previous laser bandwidth limitations. As an illustration of this capability, ketone rearrangements and dissociation reactions are considered. To introduce the experiments we discuss both optimal control theory (OCT) and optimal control experiments (OCE) with an emphasis on closed-loop control methods using near-infrared fs pulses. Because the experiments are in the strong field regime, we present the current state of the understanding of the electronic and nuclear photophysical processes that occur when polyatomic molecules are subjected to laser intensities ranging between 1013 and 1015 W cm-2. Photoelectron spectroscopy measurements are presented that begin to elucidate the control mechanisms. These delineate the order of the multiphoton process, the presence of transient shifting of excited electronic state energies (on the order of 5 eV), and the phenomena of lifetime broadening of electronic states. Recent experiments probing the energy partitioning to nuclear modes are presented with an emphasis on detecting the final kinetic energy of fragment ions. The advances in laser pulse shaping technology slaved to pattern recognition learning algorithms have opened up the prospect of studying the dynamics and chemical manipulation of virtually any system that can be introduced into the closed-loop apparatus. Rather than operating under the limitation of finding the molecule to suit the laser capabilities, the closed-loop learning control procedure operating in the strong field regime now makes it possible to merely tailor the control laser to meet the molecule's dynamical capabilities in keeping with the chemical objectives. The prospects are very bright for exploring chemical reactivity with these tools.