Zero-width resonances in intense-field molecular photodissociation

We provide additional evidence for the existence of zero-width resonances in the intense-field photodissociation of H₂⁺. In a previous investigation [Atabek, Chrysos, and Lefebvre, Phys. Rev. A 49, R8 (1994)] the situation, in a two-channel dressed picture, corresponded to a diabatic crossing point classically reachable in both adiabatic potentials. A semiclassical explanation could be modeled after that developed for predissociation in the intermediate-coupling regime. At higher frequencies the crossing point lies between the two turning points. A numerical study shows that zero-width resonances exist also in such a case. An extension of the semiclassical approach provides an explanation for the occurrence of these resonances. It is shown that they survive even when going to a multichannel description. The associated wave functions and probability densities are studied: they are very similar to those of the upper adiabatic potential, with a minor component in the lower adiabatic channel. Some conditions for the production of such long-lived dressed molecular species are stated.