We have applied Kramers-Kronig analysis to reflection spectra to determine the optical constants of ammonium hydroxide and of aqueous solutions of ammonium chloride and bromide. From considerations of the absorption indices k (<i>v</i>) we conclude that ammonium hydroxide consists of a solution of NH <sub>3</sub> in water, in which NH<sub>3</sub> molecules are hydrogen bonded to neighboring water molecules. The spectrum of ammonium hydroxide differs from the spectra of ammonium salts, in which bands characteristic of NH<sub>4</sub><sup>+</sup> ions are prominent. The existence of ammonium hydroxide as an aerosol in planetary atmospheres is briefly discussed.
© 1978 Optical Society of AmericaPDF Article