The observed and predicted spectrum of neutral chromium: Cr I

The spectrum of neutral chromium (Cr I) has been investigated in detail. It is basically a sixelectron system, exhibiting a very complex structure with its ground configuration 3 d 5 4 s . The low lying excited configuration is 3 d 5 4 p and the core excitation leads to 3 d 4 4 s 4 p . Further excitations of these configurations give rise to 3 d 5 4 d , 3 d 4 4 s 2 . In the past, a large number of levels have been reported without any satisfactory theoretical support. In the present work we have observed the spectrum of Cr on a 35 ft grating of our laboratory in the wavelength region 4800–5500 Å and have carried out configuration interaction (CI) calculations for abovementioned configurations. Known levels have been used to optimize the energy parameters of least squares fitted parametric calculations. These parameters were used to predict the unknown levels more precisely. Among 1014 energy levels, 652 levels are newly predicted (208 listed in the tables and 444 levels lying above 66500 cm −1 are available privately on demand).