Absorption Spectra of Gaseous NdBr3 and NdI3

Absorption spectra have been obtained of gaseous NdBr3 and NdI3 in the range 4000–25 000 cm−1 between 1000° and 1200°C. Spectra of solid and liquid NdI3 near the melting point have also been measured. The most prominent feature of the gaseous spectra is a complex band located between 16 000–17 000 cm−1 with oscillator strengths of 3.3×10−4 and 5.3×10−4 for NdBr3 and NdI3, respectively. The band is assigned to the hypersensitive transition 4I9/2—4G5/2. The oscillator strength of this transition in the vapor molecules is 10–50 times greater than in the solution systems studied by Carnall, Fields, and Wybourne. Various intensity mechanisms are discussed and it is concluded that the vibronic mechanism gives order-of-magnitude agreement with results. Judd's proposal that the parameter T2 is particularly sensitive to environment is borne out by the results on the vapor spectra.