A quasi-atomic treatment of the dynamics of the H2O∞-like molecule

In the framework of the Born-Oppenheimer separation between light and heavy nuclear motions, we study the dynamics of an H2O-like molecule having an infinite mass on the O nucleus: H2O∞. The motion of the two hydrogen nuclei is treated in analogy with a two-electron atom problem where the atomic orbitals are replaced by rovibronic wavefunctions of the OH molecule. The proposed approach simultaneously treats the internal and external coordinates. It is found to reproduce nicely the rotationless (J = 0) energy levels. The J = 1 energy levels and wavefunctions are analysed with reference to the rigid rotor approximation. The present work is a first step towards the treatment of the dynamics of tetra-atomic reactions involving two light and two heavy atoms.