Hyperfine structure investigations of Pr-I lines in the region 4200-4450 A

Praseodymium I spectral lines were investigated using laser induced fluorescence spectroscopy in a hollow cathode discharge lamp. The investigations led to the discovery of new Pr I energy levels of even and odd parity. A high resolution Fourier transform (FT) spectrum was used to extract promising excitation wavelengths. In the FT spectrum the investigated line 4375.53 A shows up as a narrow peak hfs with a weak SNR. Nevertheless, the line was excited and fluorescence signals were observed on 6 lines (4163 A, 4816 A, 5091 A, 5164 A, 5209 A, 5233 A). The hfs of the line was recorded by scanning the laser frequency and was fitted to obtain angular momentum J and hf constant A of the combining levels. We got Jup=5/2, Aup=1028.30 MHz, Jlo=7/2 and Alo=861.46 MHz (the subscripts refer to upper and lower level). Assuming an unknown upper level, a known lower level was searched among the known levels having sufficient values of J and A. The level 7617.440 cm-1, even parity, Jlo=7/2 and Alo=868 MHz fulfils these requirements. Using the center of gravity wave number of the line 4375.53 A and the energy of the lower level, the unknown upper level was calculated to have 30465.424 cm-1, odd parity, Jup=5/2 and Aup=1033(6) MHz.