ASSIGNING SPECTRA OF CHAOTIC MOLECULES WITH DIABETIC CORRELATION DIAGRAMS

An approach for classifying and organizing spectra of highly excited v ibrational states of molecules is investigated. As a specific example, we analyze the spectrum of an effective spectroscopic fitting Hamilto nian for H2O. In highly excited spectra, multiple resonance couplings and anharmonicity interact to give branching of the N original normal modes into new anharmonic modes, accompanied by the onset of widesprea d chaos. The anharmonic modes are identified by means of a bifurcation analysis of the spectroscopic Hamiltonian. A diabatic correlation dia gram technique is developed to assign the levels with approximate ''dy namical'' quantum numbers corresponding to the dynamics determined fro m the bifurcation analysis. The resulting assignment shows significant disturbance from the conventional spectral pattern organization into sequences and progressions. The ''dynamical'' assignment is then conve rted into an assignment in terms of ''nominal'' quantum numbers that f unction like the N normal mode quantum numbers at low energy. The nomi nal assignments are used to reconstruct, as much as possible, an organ ization of the spectrum resembling the usual separation into sequences and progressions. (C) 1996 American Institute of Physics.