Angle-resolved Rabi flopping in strong-field dissociation of molecules

Abstract

Rabi flopping is a paradigm of two-level quantum systems in the presence of an oscillatory driving field. Different from atoms, the Rabi flopping in a molecule depends on its bond length and orientation with respect to the light polarization direction. Here we explore the Rabi flopping in the strong-field dissociation of ${\mathrm{H}}_{2}{}^{+}$ in which the two lowest electronic states are photon coupled. ${\mathrm{H}}_{2}{}^{+}$ aligned along different angles experiences different laser intensities, building the Rabi flopping with angle-dependent frequencies. During the laser-${\mathrm{H}}_{2}{}^{+}$ interaction, the electron completes different fractions of Rabi flopping for ${\mathrm{H}}_{2}{}^{+}$ aligned in different directions, leading to the angular nodes and maxima in the dissociative proton momentum distribution. Our study reveals that one-photon dissociation undergoes the alternation of absorbing and emitting one photon, instead of the one-off photon absorption. This study also provides a universal explanation for the angular distribution of the dissociative fragments in strong laser fields.