Quantum calculations of highly excited vibrational spectrum of sulfur dioxide. II. Normal to local mode transition and quantum stochasticity

We report a quantum mechanical calculation of highly excited vibrational spectrum of SO2 up to 25 000 cm−1, using a filter-diagonalization method based on the Chebyshev propagation. Our results indicate a graduate transition from a normal mode regime at low energies to a local mode regime near 25 000 cm−1, which is marked by a decreasing energy gap between the (n1,0,0) and (n1−1,0,1) states and bifurcation of the corresponding wave functions. Approximately 4700 vibrational levels are found below 25 000 cm−1 and statistical analysis reveals that the SO2 vibration in this energy range is largely regular although the existence of chaos cannot be excluded.