Excited ionic states of diatomic RgH, where Rg=Kr or Xe, and their electronic transition dipoles have been characterized using the multireference configuration interaction method. The obtained results are in good agreement with the experimental observation of a very intense 6.4 eV absorption/emission in the gas phase as well as in ternary rare gas matrices containing H and Xe. Three different triatomic Xe hydrides (Xe-Xe-H, Xe-H-Xe, and triangular Xe2H) were also studied and used as model fragments for the multibody environment of the solid state. These calculations suggest that the absorptions observed in hydrogen doped solid Xe samples originate from an hydrogen atom trapped in an octahedral site. Upon vertical excitation from the van der Waals bound neutral ground state, a charge transfer configuration Xe6+H- is transiently formed and relaxes into a triatomic Xe2+H- species, which emits near 5 eV. This model is quantitatively consistent with the experimental observations.