INTRACAVITY LASER ABSORPTION SPECTROSCOPY OF HIGHLY EXCITED VIBRATIONAL STATES OF HOCI APPROACHING DISSOCIATION ENERGY.

Author Institution: Université Joseph Fourier de Grenoble, B. P. 87 38402 Saint-Martin-d'Hères Cedex France; University of Goettingen, 37077 Göttingen, GermanyLine assignments, band origins and spectroscopic constants for the excited rovibrational states of $3\nu_{1} + 2\nu_{2}$ corresponding to a five quanta transition both for $HO^{35}Cl$ and for $HO^{37}Cl$ as well as new anharmonicity parameters were obtained from completely resolved spectrum recorded for the first time using an ultrasensitive Ti:Sapphire intracavity absorption spectrometer. Transitions up to ${K^{\prime\prime}}_{a} = 5$ and ${J^{\prime\prime}} = 45$ were measured. Although this very weak a-type combination band located at $12612 cm^{-1}$ corresponds to very high internal energy of the molecule (${\sim}2/3$ of the dissociation energy), only local perturbation of the ${K^{\prime\prime}}_{a} = 4$ subband of one isotope $(HO^{37}Cl)$ due to a Fermi-type resonance with a "dark" $3\nu_{1} + 2\nu_{2} + 2\nu_{2}$ state was found. Our estimates based on the observed absorption strength and the sensitivity of the improved version of our spectrometer (ring dye laser) show our ability to record overtone bands up to the dissociation threshold in order to study intramolecular vibrational energy redistribution. The progress in this work will be also reported