Hyperfine structure of the ground state in singly ionized manganese

We report the first experimental measurements and theoretical calculations for the hyperfine splitting of the 3d5 4s ground state of Mn ii. The hyperfine structure constants were determined using Fourier transform spectroscopy with a hollow cathode discharge lamp. The uncertainties in the magnetic dipole constants, A, are between 3 × 10−4 and 5 × 10−4 cm−1. Extensive configuration interaction calculations of the hyperfine splitting of the a7S3 ground state have been carried out to compare with the experimental measurements. In addition, we give wavelengths for three resonant transitions to the ground state of Mn ii, accurate to a few parts in 108. These wavelengths are of interest in astrophysical applications such as studies of the time variation of the fine structure constant.