A Global Algebraic Treatment for XY2 Molecules : Application to D2S

We suggest to use for XY2 molecules some results previously established in a series of articles for vibrational modes and electronic states with an E symmetry type. We first summarize the formalism for the standard u(2) ⊃ su(2) ⊃ so(2) chain which, for its most part, can be kept for the study of both stretching and bending modes of XY2 molecules. Next the also standard chain u(3) ⊃ u(2) ⊃ su(2) ⊃ so(2) which is necessary, within the considered approach, is introduced for the stretching modes. All operators acting within the irreducible representation (irrep) [N00] ≡ [N u 0] of u(3) are built and their matrix elements computed within the standard basis. All stretch-bend interaction operators taking into account the polyad structure associated with a resonance !1 ≈ !3 ≈ 2!2 are obtained. As an illustration, an application to the D2S molecular system is considered, especially the symmetrization in C2v. It is shown that our unitary formalism allows to reproduce in an extremely satisfactory way all the experimental data up to the dissociation limit.