Photodissociation of NeBr2(B) below and above the dissociation limit of Br-2(B)

The photodissociation dynamics of the NeBr2 complex in the B electronic sta te is studied, for the first time, near the Br-2(B) dissociation limit, bel ow and above, when the complex is promoted from the ground T-shaped level i n the X electronic state. A time-dependent treatment is used in which the i nitial wave packet is divided in two portions, one describing the slow pred issociation dynamics below the Br-2 dissociation threshold, and the second one, the fast complete dissociation in Ne+Br+Br fragments. Below that thres hold, the absorption spectrum shows an increasing congestion as the vibrati onal energy content of Br-2 increases, but narrow peaks appear again for th e highest energy region of the spectrum. These peaks correspond to long liv ed resonances associated with "horseshoe" type states, as demonstrated by t wo-dimensional calculations. These resonances have a significant probabilit y density for the linear geometry in which the Ne atom is inserted between the two bromine atoms. At this configuration the exchange of vibrational en ergy is rather inefficient which explains both why the spectrum is so spars e and resonances are so narrow. Above the Br-2 dissociation threshold, the recombination of Br-2 is found to be very inefficient, except for very low kinetic energies. The small recombination probabilities are due to vibratio nal couplings and not to any collisional caging effect. Since the complex r emains essentially T-shaped during dissociation, extensive two-dimensional calculations are performed for longer times to better determine final vibra tional distributions at low kinetic energies. (C) 2001 American Institute o f Physics.