The FERRUM project: laboratory-measured transition probabilities for $\ion{Cr}{\fontsize{9pt}{11pt}\selectfont{II}}$

Abstract

Aims. We measure transition probabilities for Cr ii transitions from the z 4 H J , z 2 D J , y 4 F J , and y 4 G J levels in the energy range 63 000 to 68 000 cm −1 . Methods. Radiative lifetimes were measured using time-resolved laser-induced fluorescence from a laser-produced plasma. In addition, branching fractions were determined from intensity-calibrated spectra recorded with a UV Fourier transform spectrometer. The branching fractions and radiative lifetimes were combined to yield accurate transition probabilities and oscillator strengths.Results. We present laboratory measured transition probabilities for 145 Cr ii lines and radiative lifetimes for 14 Cr ii levels. The laboratory-measured transition probabilities are compared to the values from semi-empirical calculations and laboratory measurements in the literature.

The FERRUM project: Experimental transition probabilities from highly excited even 5s levels in Cr ii

“…Furthermore, neither the experimental nor the theoretical lifetimes indicate any significant J-dependence of the values. We also note that while the experimental lifetimes in the 3d 4 4p configuration are consistently longer than those calculated by Kurucz (1995) by, on the average, 37% (Nilsson et al 2006) and 22% (Gurell et al 2010) in the present case the situation is reversed and the experimental values are consistently shorter, by about 15%. A similar comparison between the 3d 4 4p lifetimes in Gurell et al (2010) and the theoretical results by Raasen & Uylings (1997) shows a perfect agreement within the error bars in all cases.…”

“…Measurements using the beam-foil technique have been reported by Pinnington et al (1973) and Engman et al (1975). The TR-LIF method has also been used in a number of previous studies (Schade et al 1990;Bergeson & Lawler 1993;Pinnington et al 1993;Nilsson et al 2006;and Gurell et al 2010), where the Cr + ions were produced in a fast ion beam, in a hollow cathode, and in laser-produced plasmas. By combining the measured lifetimes with branching fractions (BFs), usually obtained from intensity calibrated Fourier transform spectra, transition probabilities have been derived.…”

“…By combining the measured lifetimes with branching fractions (BFs), usually obtained from intensity calibrated Fourier transform spectra, transition probabilities have been derived. For example, the most recent studies by Nilsson et al (2006) and Gurell et al (2010) report 119 and 145 transition probabilities, respectively, for lines from the 3d 4 4p configuration. See Gurell et al (2010) for additional references to investigations of the 4p states.…”

The elemental composition of the Sun

“…Oscillator strengths for Cr  were recently produced by Gurell et al (2010) and Nilsson et al (2006), who each combined their own FTS BFs with accurate TRLIF lifetimes; Gurell et al (2010) used their own lifetimes, whereas Nilsson et al utilised a mixture of TRLIF lifetimes from Schade et al (1990), Bergeson & Lawler (1993a) and their own work. Unfortunately, Gurell et al (2010) the solar spectrum, we default to using the theoretical Kurucz (2011) oscillator strengths.…”

“…Unfortunately, Gurell et al (2010) the solar spectrum, we default to using the theoretical Kurucz (2011) oscillator strengths. Given that the Kurucz g f -values are known to often be inaccurate, especially for weak transitions, this is not a satisfactory situation; high-quality atomic data is urgently needed for Cr .…”