Hyperfine structure measurements for neutral and singly ionized terbium by Fourier-transform spectroscopy

Abstract

The archival data recorded by the Fourier transform spectrometer at the USA National Solar Observatory (NSO) were used to investigate the hyperfine structure (HFS) for Tb I and Tb II levels. The magnetic dipole HFS constant A values for 45 levels of Tb I ranging from 285.5 to 34 223.95 cm⁻¹ and for seven levels of Tb II below 36 602 cm⁻¹ were determined. To our best knowledge, the HFS constants for 34 out of 45 levels in Tb I and for two out of seven levels in Tb II are reported for the first time. This study extended the total number of experimentally measured magnetic dipole HFS constants A to 415 for Tb I and 92 for Tb II.