Ultrafast non-adiabatic curve crossing and energy transfer in the IBrBO+ center dot Ar van der Waals complex

Photodissociation of the T-shaped IBr B0(+). Ar complex initiated by an ult rafast laser pulse is investigated theoretically by integrating the time-de pendent Schrodinger equation for wavepacket motion in two dimensions. The f ragmentation dynamics are explored through calculations of time-dependent e xpectation values, electronic state populations and vibrational state proba bilities. The focus of this study is on the competition between electronic predissociation of IBr, induced by non-adiabatic transitions between the bo und B0(+) and repulsive Y0(+) excited states, and vibrational predissociati on of Ar from the intact diatomic, mediated by vibrational energy redistrib ution between intramolecular and van der Waals degrees of freedom. This is facilitated by comparative calculations in which non-adiabatic curve crossi ng is either included or artificially disabled. It is found that molecular dissociation to form ground-state I + Br at energies below the B0(+) asympt otic limit takes place over time scales ranging from 200-500 fs for vibrati onal levers that are strongly coupled to the Y0(+) continuum, to longer tha n 10 ps for the most metastable levels. Sequential loss of vibrational quan ta from IBr B0(+) into the van der Waals mode over a 2- 10 ps time scare is significantly disturbed by dissociation of the diatomic moiety: instead of time-ordered vibrational cooling via consecutively lower-energy levels, a complex pattern of energy transfer evolves during the lifetime of metastabl e B0(+) vibrational levels until the Ar atom is propelled into the van der Waals continuum. The probabilities of final IBr B0(+) vibrational levels ar e determined, therefore, by the strength of non-adiabatic transfer to the m olecular dissociative continuum in addition to the dynamical coupling of in tramolecular and van der Waals modes.