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F center absorption energy :an experimental study in natural sodium chloride using the method of additive coloration.
A dual purpose furnace was constructed and used to obtain F 16 3center densities up to 6 X 10 centers/cm in natural sodium chloride by additive coloration methods. The sample crystal was heated to temperatures around 600° C in a vacuum of 45 mm mercury in the presence of sodium metal vapor. The colored crystal was quenched to room tempera- ture in CH^Cl,.. and the spectrum was obtained at various temperatures. The absorption energies were obtained from direct analysis of the spectrum, and F center densities estimated from Smakula's equation assuming the oscillator strength. Experiments without quenching were performed and Na - NaCl Colloidal centers were observed. The K band and F aggregate centers, and were also present. The effects of impurities, in the natural NaCl crystals used, as seen by Mooradian (24) are not present and perhaps are due to his method of coloration by x-radiation. All results are in experimental agreement with other published results for NaCl.