Species branch of XSAMS, having four child elements, is used to represent the static properties of species, used in spectroscopy.

Species.Atoms, Species.Molecules, Species.Particles, Species.Solids elements are defined, each describing the corresponding kind of species. Atoms and Molecules may be identified by speciesID attribute, even if no state information is available, and all four kinds can be referenced by the stateID (StateIDType) attribute. In this case, for Atoms and Molecules, at least a dummy ground state needs to be created.