1 Introduction

Since 1965, experimental data of transition probabilities of singly-ionized krypton have been obtained. These data should allow researchers to obtain information about atomic structure or the type of coupling to be considered for the theoretical models. However, great discrepancies (Donnelly et al. 1975) exist in the experimental results of the different authors, as well as great uncertainties. In the last ten years there has been a renewed interest in the transition probabilities of KrII. This species has been detected in the spectra of the interstellar medium with help of the Goddard high resolution spectrograph on the Hubble space telescope (Cardelli et al. 1991; Cardelli & Mayer 1997). Krypton represents the material from which the young early type stars are formed (Leckrone et al. 1993). Moreover, krypton is present in many light source and lasers in laboratory studies and in industrial applications (Graves 1983; Mckee et al. 1996).

Although an important number of experimental works (Levchenko 1971; Miller et al. 1972; Podbiralina et al. 1973; Keil 1973; Samoilov et al. 1975; Baessler et al. 1979; Fonseca & Campos 1982; Brandt et al. 1982; Bertuccelli & Di Rocco 1991; Castro et al. 2001) and theoretical works (Koozekanani & Trusty 1969; El Sherbini 1976; Spector & Garpman 1977; Brandt et al. 1982) have been performed to determine A_ki-values for KrII, a number of lines in the spectrum exist for which there is no data.

In this work A_ki-values have been obtained in an emission experiment from measurements performed on a linear discharge lamp, where pure krypton was introduced. The plasma source employed provides not only all kinds of interferometric and spectroscopic recordings with great reproducibility in different discharges, but also makes it possible in a broad range of electron densities (0.1 to $0.8 \times 10^{23}$ m^-3) and temperatures (14000 to 24000 K). This allows us to acquire reliable spectra for weak isolated and non-isolated lines, very difficult to obtain otherwise. Absolute transition probabilities have been obtained from relative intensity measurements, taking as reference those from Fuhr & Wiese (1998) and Castro et al. (2001). In this way, the KrII excitation temperature has been determined from the Boltzmann-plot. Other techniques to calculate temperature have also been employed: KrII/KrI intensity ratios and the algorithm described in Gigosos et al. (1994). The very good agreement among these three methods suggests that the plasma is well described by a partial local thermodynamic equilibrium (pLTE) model (van der Mullen 1990). Other experimental cautions, like the existence of self-absorption or spectrometer calibration have been carefully considered. The number of measurements (12) performed for each line, and its very controlled features, allows us to obtain a very good set of A_ki-values from the mean value and its uncertainty from the standard deviation, in a spectral interval where little data exist (450-580 nm), as far as we know. These values will be compared with those found in literature.