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

We use infrared-visible double-resonance overtone excitation to prepare HOCl 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 studies on HOCl dissociation dynamics to higher energies above the dissociation threshold on the ground potential energy surface. In spite of a rapid increase of the vibrational coupling with v(OH), unimolecular dissociation is still limited by the rate at which energy initially deposited in the OH stretch leaks out into the reaction coordinate. We observe that the increased coupling 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 threshold. This implies that a microcanonical ensemble of HOCl molecules prepared even at an energy substantially higher than the dissociation threshold should exhibit non-exponential decay, contrary to the assumptions of statistical theories.