STATE-SELECTED UNIMOLECULAR DISSOCIATION OF HOCL

The unimolecular decomposition of HOCl is investigated by exciting the molecule to the region of the sixth overtone of its OH stretching vib ration (7 nu(OH)) using overtone-overtone double resonance. The excita tion scheme is sufficiently selective to allow preparation of a single angular momentum quantum state within the 7 nu(OH) vibrational manifo ld 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 dis sociation rate of k(uni)<9.4 x 10(9) s(-1) which is substantially slow er than that expected on the basis of RRKM theory. The nascent OI-I fr agment product state distribution exhibit strong oscillations which de pend on the rotational quantum numbers of the parent HOCl molecule. Fr om the measured energy release associated with the OH fragment, the he at 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.