NH3D+ ions in ammonium perchlorate: The N–D stretching bands of different sites

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Abstract
The N–D stretching region of the infrared spectrum of doped NH4ClO4 has been reexamined at low temperatures. The spectra are found to be still changing at 2 K, indicating the existence of energy differences of this order. The N–H spectrum in ND4ClO4 was also examined. Comparison of the two sets of spectra led to an assignment of the small energy differences as due to tunneling among the distinct positions the NX3Y+ ions can assume in the lattice. The distinct orientations of NH3D+ and the ND3H+ ions have slightly different energies and this, plus the tunneling, accounts for all the eight observed lines. A complete assignment of the tunneling levels will, however, require more information.