Laboratory atomic transition data for precise optical quasar absorption spectroscopy

Quasar spectra reveal a rich array of important astrophysical information about galaxies which intersect the quasar line of sight. They also enable tests of the variability of fundamental con-stants over cosmological time and distance-scales. Key to these endeavours are the laboratory frequencies, isotopic and hyperfine structures of various metal-ion transitions. Here we review and synthesize the existing information about these quantities for 43 transitions which are im-portant for measuring possible changes in the fine-structure constant, α, using optical quasar spectra, i.e. those of Na, Mg, Al, Si, Ca, Cr, Mn, Fe, Ni and Zn. We also summarize the infor-mation currently missing that precludes more transitions being used. We present an up-to-date set of coefficients, q, which define the sensitivity of these transitions to variations in α. New calculations of isotopic structures and q coefficients are performed for Si ii and Ti ii, includ-ing Si ii λ1808 and Ti ii λλ1910.6/1910.9 for the first time. Finally, simulated absorption-line spectra are used to illustrate the systematic errors expected if the isotopic/hyperfine structures are omitted from profile fitting analyses. To ensure transparency, repeatability and currency of the data and calculations, we supply a comprehensive database as Supporting Information. This will be updated as new measure-ments and calculations are performed