Laser-driven nonadiabatic electron dynamics in molecules

In this review, we briefly summarize more than a decade of experimental and theoretical investigations regarding the nonadiabatic electron response to intense femtosecond duration laser fields in a variety of molecular systems. Historically, experimental signatures of nonadiabaticity have emerged readily in large, conjugated, or multi-electron systems, disrupting fragmentation behavior and modulating observed rates of ionization. As model theoretical studies performed in H2+ and other diatomic species show, departure from traditional quasi-static or cycle-averaged descriptions of laser-induced ionization is often necessary to accommodate the rich and frequently counterintuitive electron dynamics that characterize the nonadiabatic response. Nonadiabatic effects such as transient electron localization or the observation of multiple ionization bursts per driving field cycle possess the capacity to modulate the signal of many strong-field physical effects, such as high-order harmonic generation, photoelectron momentum distributions, and molecular fragmentation products. As the advancement of experimental technologies expands the pursuit of laser-driven physics further into the mid-infrared wavelength regime, we suggest that these nonadiabatic effects will become increasingly pronounced and relevant to the imaging and control of a wide array of molecular species.