Extended Analysis of Cr IV

The continued analysis of the spectrum of three-times-ionized chromium, Cr IV, has led to the identification of levels of the 3 d 2 4 d and 3 d 2 5 s configurations and to improved energy values for the levels of 3 d 3 , 3 d 2 4 s and 3 d 2 4 p . The previously unknown level 3 d 2 ( 1 S )4 s 2 S 1/2 has also been found. From 741 observed lines from 523 Å to 2423 Å, we have established 154 of the 163 possible levels of the 3 d 3 , 3 d 2 4 s , 3 d 2 4 p , 3 d 2 4 d and 3 d 2 5 s configurations with an estimated uncertainty of less than 0.4 cm -1 . The results are based on spectrograms obtained by means of a low-voltage sliding-spark discharge and the 10.7 m normal incidence spectrograph at the National Bureau of Standards in Washington DC and the 3 m normal incidence spectrograph at our institute. The level structure of the five configurations has been theoretically interpreted. The energy parameters are determined by least-squares fits to the observed levels and by Hartree-Fock calculations. The ionization energy is estimated to be 396 500 ± 400 cm -1 (49.16 ± 0.05 eV). Predicted wavelengths and intensities for the forbidden transitions within the 3 d 3 configuration are collected in a list containing 52 entries from 2596 to 7664 Å.