Vibrational predissociation of ArCl2: Toward the determination of the potential energy surface of the B state

Accurate quantum mechanical calculations are carried out to test the sensitivity of the spectroscopy and dynamics of the B state of ArCl2 to the steepness of the Morse term, alpha, of an atom-atom potential. It is discovered that the predissociation dynamics for this molecule are very complicated even in the Delta v=-1 regime due to resonances in the continuum manifold of states. In both the Delta v=-1 regime and the Delta v=-2 regime the rate of vibrational predissociation and the product rotational distribution are extremely sensitive to the value chosen for alpha, but not in a regular way. For the Delta v=-2 regime the variations can be attributed to spacings between resonances and the overlaps of the bright state wave functions with nearby dark states as expected from the intramolecular vibrational relaxation model. In the Delta v=-1 regime, the variations are shown to originate from resonances in the v-1 continuum set of states. Although this makes it difficult to determine the value for alpha, a value of 1.8 Angstrom(-1) is probably close to the true value. The most useful new data to determine the potential would be measurements of the lifetimes for as many vibrational levels as possible and rotational distributions for excitation to low vibrational levels of the B state. (C) 1996 American Institute of Physics.