Knowledge Bank

We have improved the perturbation technique used in diagonalizing the non-rigid bender Hamiltonian of Ref. (1). By fitting (in a single fit) the eigenvalues of this effective rotation-bending Hamiltonian to the observed rotation energy levels (J=0 up to 10) in the $(v1,v2,v3)=(0,0,0)$ and (0,1,0) states of $H2O$ and $D2O$ we have refined the equilibrium geometry and force field. We have also calculated these energy levels using the ab initio equilibrium geometry and force constants of Ref. (2), and this is then the first complete ab initio calculation of rovibrational energy levels of high J in a polyatomic molecule to this precision.