 Because of this symmetry and the fact that it has a dipole moment, the rotational selection rules are Δ"J" = ±1 and Δ"K" = 0.The transition dipole lies along the "c"-axis and, because the negative charge is localized near the oxygen atom, the dipole moment points to the apex, perpendicular to the base plane.Hydronium is the cation that forms from water in the presence of hydrogen ions.