The absorption spectra of Pr2(SO4)3·8H2O were photographed when the salt was at 20°K, 78°K, 105°K, 169°K, 200°K and 300°K. At least three low lying excited levels were found to exist beside the basic one and they appear to be located at 110, 235 and 500 cm—1above the basic state. They are therefore in fair agreement with the calculations of Penney and Schlapp and with the field constantDfor the rare earth sulphates which was determined spectroscopically for Nd and Er. A very strong coupling of vibrational states with the highly excited energy states seems to occur as the absorption bands consist of hundreds of closely spaced lines.
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