Several theoretical models are used to explain the origin of the recently observed (unexpected) spectral progression in the Coulomb explosion spectra of the hydrogen molecule photoionized by an intense ultrashort laser pulse. In the first ionization step the molecule loses its first electron and then the $\mathrm{H}_2{}^{+}$ molecular ion dissociates. Next, at the intermediate stage of the dissociation process, a localized electron state is created from which the second ionization occurs at each laser half-cycle. It is shown that interference between a net-two-photon and a one-photon transition introduces a dynamic structure into the nuclear wave packet corresponding to this localized electron state which leads to the regular spectral progressions seen in the experiment. We confirm these spectral progressions using numerical simulations based on a time-dependent Schrödinger equation describing the exact three-body dynamics of $\mathrm{H}_2{}^{+}$ in one dimension.

• Received 2 June 2007

DOI:https://doi.org/10.1103/PhysRevA.76.013405