Eigenstate-resolved unimolecular dissociation dynamics of HOCl at v(OH)=7 and 8

We use infrared-visible double-resonance overtone excitation to prepare HOC l molecules in single, well-characterized rotational levels of the high OH stretching states v(OH) = 7 and v(OH) = 8. This work extends our recent stu dies on HOCl dissociation dynamics to higher energies above the dissociatio n threshold on the ground potential energy surface. In spite of a rapid inc rease of the vibrational coupling with a,,, unimolecular dissociation is st ill limited by the rate at which energy initially deposited in the OH stret ch leaks out into the reaction coordinate. We observe that the increased co upling is not sufficient to put the molecule in the statistical limit, even at the energy of v(OH) = 8, which is 5000 cm(-1) above the dissociation th reshold. This implies that a microcanonical ensemble of HOCl molecules prep ared even at an energy substantially higher than the dissociation threshold should exhibit non-exponential decay, contrary to the assumptions of stati stical theories.