Lifetimes of metastable levels of singly ionized titanium: theory and experiment

This paper presents new theoretical lifetimes of metastable levels in singly ionized titanium, Ti II. Along with the lifetimes, transition probabilities for several decay channels from these metastable levels are presented. The calculations are supported by experimental lifetime determinations of the 3d(3) b (2)D(5)/2 and 3d(2)((3)P)4s b (2)P(3)/2 levels along with revised values of the previously published lifetimes of the 3d(2)((3)P)4s b (4)P(5)/2 and 3d(2)((3)P)4s b (2)P(1)/2 levels originating partly from a reanalysis utilizing a recently developed method applied on the previously recorded data and partly from new measurements. The presented theoretical investigation of lifetimes of metastable levels in Ti II shows that the HFR calculations are in general compatible with measurements performed using the ion storage ring CRYRING of Stockholm University. The transition probabilities of forbidden lines derived from the new lifetime values will be useful for the diagnostics of low density laboratory or astrophysical plasmas, particularly those encountered in the strontium filament found in the ejecta of eta Carinae.