Experimental Studies on Electronic Configuration Mixing for the Even-Parity Levels of Gd I Using Isotope Shifts Recorded in the Visible Region with FTS
Electronic configuration (4f76s26p + 4f75d6s6p + 4f75d26p) mixing studies in the high even-parity energy levels of Gd I spectrum have been carried out on the basis of isotope shift (IS) data recorded in 49 spectral lines partially in the visible wavelength region on Fourier Transform Spectrometer (FTS) and the relevant spectral line IS data available in the literature. We employed “Sharing rule” to the experimentally observed level isotope shifts (LIS) of the even-parity levels for finding the percentage composition of each configuration being mixed. An FTS spectrum of Gd I in the region of 365–495？nm acquired employing the highly enriched Gd isotopes in liquid nitrogen cooled hollow cathode lamp (HCL) as a light source and photomultiplier tube as the detector. The studies of altogether 48 even-levels have revealed that amongst the 20 high even parity levels assigned previously to >95% 4f75d6s6p configuration, 10 levels have agreed very well whereas 7 have exhibited large contribution of 4f75d6s6p configuration compared to 4f75d26p configuration and 3 levels have equal contribution of 4f75d6s6p and 4f75d26p configurations. Out of 8 unassigned levels, 6 have dominant 4f75d6s6p configuration compared to 4f75d26p configuration and the remaining two have dominancy in 4f75d26p configuration. 1. Introduction Gadolinium occupies position in the middle of the lanthanide series and has the [Xe] 4f75d6s2 ground state configuration generating highly complex first spectrum of neutral gadolinium atom (Gd I) [1]. For the last few decades many successful attempts have been made to investigate the Gd I spectrum. Albertson [2] in 1935 identified 5 low odd-parity levels of ground term and 35 upper even-parity levels comprising 71 classified spectral transitions. Analyses of arc and spark spectra based on wave numbers and intensities by Russell [3] have led to the energy level classification of 1217 transitions of Gd I with identification of some 200 even-parity levels. Although enriched Gd isotopes have been employed by Speck [4] for the first time for studying IS in the Gd I spectrum their data was confined mainly to investigate the nuclear spins and moments of odd isotopes. Odintsova and Striganov [5] reported IS between all pairs of even isotopes in many strong spectral lines for the first time; however the data was limited to the studies of static deformation parameter and internal quadruple moment for the nucleus of Gd-152 isotope. Electronic configuration assignment studies have been performed on Fabry-Perot Spectrometer (FPS) employing IS as a tool in this
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