Editing Hydronium (section)

==Structure==
Since {{chem2|O+}} and N have the same number of electrons, {{H3O+}} is [[isoelectronic]] with [[ammonia]]. As shown in the images above, {{H3O+}} has a [[trigonal pyramidal molecular geometry]] with the oxygen atom at its apex. The {{chem2|H\sO\sH}} [[bond angle]] is approximately 113°,<ref>{{cite journal | title = Infrared spectroscopy of H<sub>3</sub>O<sup>+</sup>: the v<sub>1</sub> fundamental band | first1 = Jian | last1 = Tang |first2 = Takeshi | last2 = Oka | journal = [[Journal of Molecular Spectroscopy]] | volume = 196 | pages = 120–130 | year = 1999 | doi = 10.1006/jmsp.1999.7844 | pmid = 10361062 | issue = 1| bibcode = 1999JMoSp.196..120T}}</ref><ref>{{cite book| last1 = Bell | first1 = R. P. | page = 15 | edition = 2nd | title = The Proton in Chemistry | publisher = Cornell University Press | location = Ithaca | date = 1973 }}</ref> and the center of mass is very close to the oxygen atom. Because the base of the pyramid is made up of three identical hydrogen atoms, the {{H3O+}} molecule's [[symmetric top]] configuration is such that it belongs to the {{chem2|C_{3v}|}} [[Point groups in three dimensions|point group]]. Because of this symmetry and the fact that it has a dipole moment, the rotational [[selection rule]]s are Δ''J''&nbsp;=&nbsp;±1 and Δ''K''&nbsp;=&nbsp;0. The [[Transition dipole moment|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.