In this Brief Report an improved u(2) algebraic model is proposed to study both stretching and bending vibrational spectra of a bent triatomic molecule. The model with fewer parameters is used to reproduce the observed spectra of hydrogen sulfide (H${}_{2}$S) with better precision than the u(4) algebraic model. Furthermore, the tripartite entanglement dynamics is investigated for vibrationally localized states in H${}_{2}$S. It is shown that the entanglement of a highly excited state in the bending mode displays better quasiperiodicity than that in the stretch. Those are useful for molecular vibrations and multipartite quantum entanglement.