Infrared Reflection Spectra of Phosphate and Arsenate Crystals

Abstract

Crystals of KH₂PO₄, NH₄H₂PO₄, KH₂AsO₄, and NH₄H₂AsO₄ were examined in the 1—25 micron region. Data were obtained at room temperature for all four crystals, and in addition the spectra of the potassium compounds were examined below their Curie points. In order to avoid the use of thin crystal cuts required for absorption measurements, an optical system was designed which permitted recording of reflection spectra. At the low temperature an increase in the number of bands was observed, and the phosphate and arsenate spectra seemed displaced to higher frequencies. The transition from hydrogen bonding prevailing at room temperature to hydroxyl bonding below the Curie points is considered likely.