Abstract
A new method for the calculation of rovibrational wavefunctions and energy levels of molecules is presented. In this method the Hartree separation scheme is applied in order to reduce the rovibrational Schrödinger equation to coupled vibrational and rotational equations. They are solved in a self-consistent way. The method allows the determination of a centrifugal potential describing the influence of rotations on the internal motions in a molecule. The theory presented is tested on the formaldehyde molecule which is nonrigid in the à 1 A 2 electronic state. The results obtained indicate that our approach is more effective and accurate than the standard variational approach.