The unimolecular decomposition of HOCl is investigated by exciting the molecule to the region of the sixth overtone of its OH stretching vibration (7 nu(OH)) using overtone-overtone double resonance. The excitation scheme is sufficiently selective to allow preparation of a single angular momentum quantum state within the 7 nu(OH) vibrational manifold lying similar to 2500 cm(-1) above the dissociation limit. From the measured linewidths associated with the rotational features appearing in the action spectrum, we obtain an upper limit estimate for the dissociation rate of k(uni)<9.4 x 10(9) s(-1) which is substantially slower than that expected on the basis of RRKM theory. The nascent OI-I fragment product state distribution exhibit strong oscillations which depend on the rotational quantum numbers of the parent HOCl molecule. From the measured energy release associated with the OH fragment, the heat of formation of HOCl is estimated to be Delta H-0(0)(0 K) = -16.7 +/- 0.6 kcal/mol. (C) 1997 American Institute of Physics.