LINE ABSORPTION IN THE INFRARED SPECTRUM OF SODIUM CHLORIDE CRYSTALS

Author Institution: General Electric Company, Research Laboratory SchenectadyMost artificial NaCl crystals which have been obtained from Harshaw in the past few years have very sharp absorption lines at 1997 and $2067 cm^{-1}$. Half width of the lines is $1.2 cm^{-1}$ at room temperature. At low temperature, the lines shift to higher frequency and become narrower; peak intensity passes through it maximum between 120 and $160^{\circ} K$. Variations in intensity of the spectra for different parts of the same crystal indicate that the lines are connected with the presence of impurities. The lines are bleached completely by x-rays, but ran subsequently be regenerated by heating to $300 160^{\circ} C$. They are bleached permanently by diffusing $Cal^{++}, Cd^{++}, Ni^{++}, Mn^{++}, and Cu^{++}$ into crystals at $700^{\circ}C$. Various models for the absorbing center will be considered