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Experimental branching fractions (BFs) of Mo II, ranging in wavelength from 1970 to 4370 Å, have been measured from intensity calibrated spectra recorded with the Lund UV Fourier transform spectrometer (FTS). Radiative lifetimes for 10 levels have been measured using the method of laser-induced fluorescence (LIF). Combining BFs with new as well as previously measured lifetimes, 16 in total, oscillator strengths of 91 lines were derived. Seven transitions are resonance lines involving the ground state. The BF results are compared with calculations made with the Cowan code and the f-values are compared with previously published data. Improved wavelengths from an ongoing term analysis are also reported.

Radiative lifetimes of two levels in Ce I, eight levels in Ce II, and nine levels in Ce III have been measured using the time-resolved laser-induced fluorescence technique. Free cerium atoms and singly and doubly ionized ions were obtained in a laser-produced plasma. A narrow bandwidth UV laser pulse was employed to selectively populate the short-lived upper levels and the lifetime values were evaluated from the time-resolved fluorescence signals recorded by a fast detection system. Transition probabilities for Ce III were obtained from branching fractions calculated by the Cowan code and the experimental lifetimes. The results are compared with previous measurements and calculations. Spectral lines of Ce III were identified in the spectrum of the magnetic chemically peculiar star ␣ 2 CVn and the abundance of cerium was determined from synthetic spectrum fitting to be 800 times greater than the solar abundance.

Abstract.We report on measurements of radiative lifetimes in singly ionized iron of six 3d 6 4p levels between 61 512 and 64 041 cm −1 , using time-resolved laser-induced fluorescence. Absolute oscillator strengths of 18 Fe II lines in the wavelength range from 2350 to 2800 Å have been obtained by measuring branching fractions for the lines from two Fe II levels with a Fouriertransform spectrometer. The uncertainty in the lifetimes is between 8% and 13%, whereas the uncertainty of the f -values varies between 9% and 19%. A comparison with several previously published values is given.

We present the FERRUM Project, an international collaboration aiming at a production and evaluation of oscillator strengths (transition probabilities) of selected spectral lines of singly ionized iron group elements, that are of astrophysical relevance.The results obtained include measurements and calculations of permitted and forbidden lines of Fe II. The data have been applied to both emission and absorption lines in astrophysical spectra. We make comparisons between experimental, theoretical and astrophysical f-values. We give a general review of the various measurements, and discuss the UV8 multiplet of Fe II around 1610 Ð in detail.