Fourfold Clusters of Rovibrational Energies in H2Po Studied with anab InitioPotential Energy Function

Abstract

We report here anab initioinvestigation of the cluster effect (i.e., the formation of four-member groups of nearly degenerate rotation–vibration energy levels at higherJandKavalues) in the H2Po molecule. The potential energy function has been calculatedab initiofor a total of 143 molecular geometries by means of the CCSD(T) method, using an averaged relativistic effective potential for Po in conjunction with a newly optimized basis set. The values of the potential energy function obtained cover the region up to around 5000 cm−1above the equilibrium energy. On the basis of theab initiopotential, the rotation–vibration energies of H2209Po have been calculated with the MORBID (Morse oscillator rigid bender internal dynamics) Hamiltonian and computer program. In particular, we have calculated the rotational energy manifolds forJ≤ 40 in the vibrational ground state. We find that the formation of fourfold clusters in H2Po is very similar to that in H2Te.