Vibrationally assisted dissociative ionization of H2+ in orthogonal laser fields

We present full-dimensional quantum simulations of H2+ dissociative ionization driven by strong orthogonal laser fields. We consider equal-frequency orthogonal components, which generate elliptical or circular polarization, depending on their relative phase and amplitude, as well as orthogonal 800 and 400 nm two-color fields. These two-dimensional fields strongly modify the fragmentation dynamics. Most notably, a secondary proton kinetic-energy-release (KER) peak at approximately 4-5 eV, generally negligible in height relative to the main peak in the single-color, linearly polarized reference, is strongly enhanced by the orthogonal fields studied here and becomes pronounced and comparable in height with the main peak. The yield of this peak can be coherently controlled by varying the relative carrier-envelope phase of the perpendicular field component. The perpendicular field also disrupts the clear electron-proton energy-sharing pattern observed in the main 3-3.5 eV dissociation channel, indicating more complex multichannel dynamics. Time-dependent state projections and calculations initiated from individual excited states attribute the additional peak to laser-induced vibrational excitation of H2+. The added high-KER yield provides a concrete microscopic mechanism that may contribute to the broader, flatter proton KER distribution observed experimentally under circular polarization, even when the secondary peak is not individually resolved. Furthermore, the perpendicular field rotates the fragment angular distributions, causing the most probable proton and electron emission directions to deviate substantially from the principal z axis. These findings demonstrate that the spatial and temporal geometry of orthogonal laser fields provides an additional degree of freedom for controlling ultrafast electron-nuclear dynamics.