ANHARMONIC COLLECTIVE VIBRATIONAL-MODES IN AB-A-TRIATOMIC MOLECULES

An algebraic Hamiltonian for two coupled anharmonic (Morse-type) oscillators admits an exact symmetry at a finite value of the coupling constant. The two symmetry-adapted modes are neither local nor normal, yet are independent. The explicit discussion is given for two coupled stretch modes but the same symmetry is found also when the two stretches are in addition coupled to the bend mode. © 1990 The American Physical Society.