Quantum monodromy in the spectrum of H2O and other systems: new insight into the level structure of quasi-linear molecules

The concept of quantum monodromy is introduced to give insight into the ene rgy levels of systems with cylindrically symmetrical potential energy barri ers. The K structure of bending progressions of bent molecules and the pend ular states of dipolar molecules in strong electric fields are taken as mol ecular examples. Results are given for a two-dimensional champagne bottle m odel, for six computed bending progressions for water taken from the compil ation of Partridge and Schwenke and for the quantal spherical pendulum. Sha rp changes in the energy level patterns around the barrier energy are relat ed to changes in the forms of the relevant classical trajectories. Analytic al insight into the mathematical origin of the monodromy are also given.