SPECTROSCOPIC INVESTIGATION OF THE GENERATION OF ``ISOMERIZATION'' STATES OF HCP: EIGEN-VECTOR ANALYSIS OF THE BEND- CP STRETCH POLYAD

Abstract

Highly excited vibrational levels of HCP, in which bend-CP stretch polyads are the most fundamental vibrational structure, have been investigated by dispersed fluorescence and stimulated emission pumping spectroscopies. $HCP \longleftrightarrow CPH$ system is a prototype of the isomerization reaction of triatomic monohydride. HAB, that is the most simplest bond-breaking isomerization. Simulated by the experimental observation of vibrational levels with rotational constants (B-values) 5-10\% larger than other observed $leels,^{a}$ Schinke and coworkers noticed that these large-B levels were characterized by atypical nodal structures indicative of large amplitude motion along the minimum energy $HCP \longleftrightarrow CPH$ isomerization $path.^{b}$ Vibrational levels having such nodal structures can be referred to as ``isomerization'' levels. In order to elucidate the generation of the ``isomerization'' states, a global least squares fit, based on a traditional spectroscopic (algebraic) effective Hamiltonian polyad model, was carried out. An analysis of eigenvectors of the Hamiltonian matrix shows that all of the observed ``isomerization'' states belong to polyads and that the eigenvectors of this $H^{eff}$ model have the qualitatively distinct nodal structure first noticed by Schinke and coworkers. The ``isomerization'' states are not indicative of a breakdown of the polyad model; rather they are a natural consequence of this traditional spectroscopic model.