Algebraic approach to vibrationally highly excited states of SO2. Vibrational wavefunctions from spectroscopy

A total of 311 vibrational level energies of SO2 in the electronic ground state obtained from dispersed fluorescence spectroscopy are fitted to the algebraic Hamiltonian expansion and Dunham-type expansion. A comparison of the results of the numerical fits up to 20407 cm−1 shows that the algebraic approach developed by Iachello, Levine and co-workers is more appropriate than the Dunham-type expansion for describing vibrational level energies in a wide energy range covering the vibrationally highly excited region. It is demonstrated that the vibrational wavefunctions can be constructed directly from the algebraic fit to the experimental data, and that the characteristic bifurcation of the vibrational wavefunctions is identified in the excitation of the symmetric stretching mode. This bifurcation is interpreted as a transition from normal-mode to local-mode behavior on the basis of finding a local-mode doublet representing the vibrational energy flow between the two SO bonds.