DOUBLE-RESONANCE OVERTONE PHOTOFRAGMENT SPECTROSCOPY OF trans-HONO

Abstract

Three OH-overtones $(5\nu_{1}, 6\nu_{1}$ and $7\nu_{1})$ of trans-HONO have been investigated using double resonance overtone photofragment spectroscopy. The obtained double resonance spectra contained rich information about molecular constants, intramolecular dynamics, and lifetimes of the highly excited transient molecules. From the J and K dependence of the overtone spectra the dissociation threshold could be determined with high precision $(E_{0}=16786.7\pm 0.6 cm^{-1})$. In addition, rotational constants, band origins, perturbations, dissociation rates, and product state distributions have been determined. The linewidths of single resonances and the product state distributions have been compared with predictions from statistical theories like SACM and PST. The molecule excited in individual overtones showed different intramolecular dynamics, depending upon the number of quanta in $\nu_{1}$. The number and the strength of intramolecular (low-order) couplings to dark background states was found to increase with increasing OH excitation. However, even in the case of $7\nu_{1}$ the rotational structure was still found to be regular which suggests that the zeroth-order OH-stretching mode is only weakly coupled to other vibrations of the molecule. A full analysis of the different intramolecular couplings, mechanisms of intramolecular dynamics, and excited state lifetimes in different overtones of $\nu_{1}$ of trans-HONO above the dissociation threshold will be presented at the conference.