f-Value Measurements for 3d-Elements

We give a survey of data on transition probabilities of allowed lines that belong to the spectra of neutral and singly-ionized iron-group elements. The classical methods used to determine oscillator strengths of weak lines (usually on a relative scale) are reviewed and some of the difficulties arising in investigating the spectra of 3 d -elements are pointed out. The quality of experimental lifetimes and f -values of strong lines, i.e., of data which are frequently used to establish absolute scales, are discussed in the context of the methods employed. The results on weak lines are then assessed, element by element, and some applications are mentioned. It is concluded that further, more precise measurements are needed, since a given oscillator strength of a weak line is, in most cases, known within a factor of 1.5 or 2 only. The importance of confirming existing data is stressed. An urgent need is found to exist for better data on singly-ionized 3 d -elements.