Dipole Moment of PO<span style=text-decoration:overline><sup>3</sup><sub>4</sub></span><sup>-</sup> and NH<span style=text-decoration:overline><sup>+</sup><sub>4</sub></span> Ions of NH<sub>4</sub>H<sub>2</sub>PO<sub>4</sub> in the Paraelectric Phase.