The strong-field control of IBr photodissociation re-visited

The photodissociation of IBr is a paradigm for a process that can be controlled by a strong, non-resonant electric field, known as the non-resonant dynamic stark effect (NRDSE). As shown by B. J. Sussman <i>et al.</i>, <i>Science</i>, 2006, <b>314</b>, 278, a carefully timed intense infra-red pulse can enhance or reduce the flux into the different dissociation channels. This was supported by quantum dynamics simulations using a 3-state model of IBr, but these were unable to reproduce the experimental time-scales. In this paper, we revisit this pump-control scenario using quantum dynamics simulations including all 36-states of IBr in a coupled manifold, with potentials and couplings depending on the applied field strength, <i>i.e.</i> including the light-molecule interaction to all orders. The results reproduce the features of the experimental control, with a better fit to the time-scale than previous simulations. The mechanism by which the control operates is then found be a combination of excited-state excitation and modulation of the avoided crossing on the dissociation pathway.