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Isotope shift ∆σ( 156 Gd-160 Gd) is reported in 70 spectral lines of neutral gadolinium atom (Gd I) in the 3290-3920Å region providing isotope shift data in UV lines of Gd I spectrum for the first time. The measurements were carried out on a photoelectric recording Fabry-Perot Spectrometer using highly enriched isotopic samples of gadolinium. Term isotope shifts ∆T ( 156 Gd-160 Gd) have been evaluated for 48 high lying even parity energy levels of Gd I using this data; new ∆T values have been obtained for 24 levels. Electronic configurations 4f 7 5d6s6p, 4f 7 5d 2 6p and 4f 8 5d6s assigned earlier to these even levels have been either confirmed or configuration mixing pointed out in some of these levels. Probable assignment of 4f 8 5d6s configuration to 8 even levels between 32 930 and 35 500 cm −1 have been confirmed.

Isotope shift (IS) (142-150) have been measured in 92 spectral lines of Nd> in the region 3290-3955 A s , employing recording Fabry-Perot spectrometer and highly enriched isotopic samples excited in a liquid-nitrogen cooled hollow cathode. Earlier IS measurement in UV region of Nd II spectrum is available for only a few lines, New classification has been made for several of the spectral lines studied presently. We have also revised the earlier suggested classification for some of the Nd II lines on the basis of observed isotope shifts. The transitions presently studied mostly involve high lying odd parity energy levels above 30,000 cm\ having neither electronic configuration assignment nor term isotope shifts ( ¹ ) evaluated. The present study would thus enable to evaluate ¹ values of some of these high lying odd levels, which should be helpful in suggesting possible electronic configurations.

A Schiff base, namely, 4-[(2-hydroxy-3-methoxybenzylidene) amino] benzoic acid (L1), has been synthesized by the condensation reaction. It has been characterized by Fourier transform infrared spectroscopy , UV–vis spectroscopy, single-crystal X-ray diffraction, and DFT/B3LYP calculations. Single-crystal X-ray crystallographic analysis revealed that L1 exists in the zwitterionic (N–H···...O) form. The supramolecular interactions were investigated by Hirshfeld surface analysis. In addition, third-order nonlinear optical (NLO) properties of L1 were also investigated. The nonlinear refractive index (n2), nonlinear absorption coefficient (β), and the third-order NLO susceptibility (χ(3)) have been estimated at different concentrations and at different laser powers using close and openaperture Z-scan data. The values of the parameters were found to be varying almost linearly with concentration and power. The present study revealed the utility of the material for various optoelectronic devices such as optical switches, optical data storage devices, and optical sensors. The optical limiting study reveals that this material can also be exploited as an instrument protector from unwanted laser illumination. Furthermore, the NLO behavior of L1 has also been studied by B3LYP/6-311++G­(d,p) results.

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