Knowledge Bank

$NH4Cl$ and $NH4Br$ are well known to have order-disorder transitions. The infrared and Raman spectra have been investigated above and below these transitions and the modes observed have been interpreted in terms of the low frequency lattice vibrations. The infrared reflectivity measurements have been treated with a Kramers-Kronig and classical dispersion analyses to obtain the optical constants, frequencies, oscillator strengths, damping constants and effective charges as a function of temperature. The work of the Spectroscopy Laboratories is supported in part by the National Science Foundation, Grant No. GP4923.