Theoretical investigation of the lower bend-stretch states of the Cl−H2 anion complex and its isotopomers

Coupled-cluster [CCSD(T)] calculations of the potential energy surface of the Cl−H2 complex were carried out, subsequently averaged over the vibrational motion of the H2 moiety and then fitted. The lower bend-stretch levels of the anion complex were then determined, for the H2 molecule in its ground and first excited vibrational levels. The resulting rotational constants agree with earlier experimental values, almost to within the experimental precision. The predicted dissociation energies are 5–8% larger than the experimentally derived values. The bend-stretch wave function of the lowest state of the Cl−oD2 complex encompasses a considerably larger range of bending motion than in the complexes with oH2 and pD2.