State-resolved intramolecular dynamics in highly excited HOCl

The features and mechanisms of intramolecular energy redistribution (IVR) and state mixing of HOCl at chemically significant energies have been investigated using intra-cavity laser absorption spectroscopy (ICLAS). These studies revealed that for the observed vibrational stales up to about 75% of the dissociation energy E(0) both strong and weak interactions (Fermi-type, Coriolis) exist but producing only localized perturbations in the spectra. The 5 nu(1) band, however, at about 85% of the dissociation threshold E(0) (O-Cl bond) has been found to be globally and strongly mixed with the 4 nu(1) + 2 nu(2) + nu(3) zero-order vibrational state, and both states appeared in turn coupled to other background states by additional (weaker) interactions. The transfer from frequency to time domain led to the conclusion that this spectral signature is characteristic for efficient but nevertheless restricted intramolecular vibrational energy redistribution in the overtone spectrum of HOCl. The intramolecular dynamics of HOCl is compared to the dynamics of HCN and discussed in terms of low-order interactions between zero-order states (ZOS) grouped in different tiers.