HIGH-TEMPERATURE SPECTRA OF AQUEOUS TRANSITION METAL SALTS .I. PRASEODYMIUM AND NEODYMIUM NITRATE TO 356 DEGREES

The visible spectra of aqueous Pr(NO3)3 and Nd(NO3)3 have been recorded to 356°. The integrated areas of the absorption bands have been analyzed with respect to changes caused by temperature and hydrolysis, and similarities to corresponding spectra from organic solutions have been observed. The areas of the two Pr3+ spectral band groups decrease by 40 and 60%, and the transition energies remain constant when the temperature is increased to 356°. The temperature effects on the Nd3+ spectral bands are more dramatic. One new band observed above 290° results from the thermal population of an energy level above the usual ground state. The area of the Nd3+ hypersensitive band at 5754 Å increases by a factor of ∼5 when the temperature is increased from 25 to 356°. This increase appears to be the result of a change in the vibration effects on the Nd3+ ion as the ion is dehydrated. The changes in the area and position of the hypersensitive band are linear functions of temperature with changes in slope at 90 and 240°.