Optical isotope shifts have been measured in 11 lines of the neutral-tantalum spectrum. The tantalum atoms were introduced into a hollow cathode discharge, whose cathode wall was covered with 4 mg of a ${\mathrm{Ta}}_2$${\mathrm{O}}_5$ sample containing ${}_{}{}^{180}{}_{}{}^{}\mathrm{Ta}$ enriched to 4.1%. Using laser excitation with either optogalvanic or laser-induced fluorescence detection, the hyperfine constants of the levels involved and the shifts of the centers of gravity between ${}_{}{}^{180}{}_{}{}^{}\mathrm{Ta}$ and ${}_{}{}^{181}{}_{}{}^{}\mathrm{Ta}$ could be determined. The measurements show differences in the level isotope shifts within the terms ${}_{}{}^6{}_{}{}^{}\mathrm{D}$, z ${}_{}{}^6{}_{}{}^{}\mathrm{D}_{}^{\mathrm{o}}{}_{}{}^{}$, y ${}_{}{}^4{}_{}{}^{}\mathrm{D}_{}^{\mathrm{o}}{}_{}{}^{}$, and ${}_{}{}^4{}_{}{}^{}\mathrm{P}_{}^{\mathrm{o}}{}_{}{}^{}$: ΔT{5${\mathit{d}}^4$(a ${}_{}{}^5{}_{}{}^{}$D)6s ${}_{}{}^6{}_{}{}^{}\mathrm{D}_{3/2}^{}{}_{}{}^{}$–${5\mathrm{d}}^4$(a ${}_{}{}^5{}_{}{}^{}\mathrm{D}$)6s ${}_{}{}^6{}_{}{}^{}\mathrm{D}_{1/2}^{}{}_{}{}^{}$}=527(35) MHz, ΔT{5${\mathit{d}}^3$6s(a ${}_{}{}^5{}_{}{}^{}$F)6p ${}_{}{}^6{}_{}{}^{}\mathrm{D}_{3/2}^{\mathrm{o}}{}_{}{}^{}$–${5\mathrm{d}}^3$6s(a ${}_{}{}^5{}_{}{}^{}\mathrm{F}$)6p z ${}_{}{}^6{}_{}{}^{}\mathrm{D}_{1/2}^{\mathrm{o}}{}_{}{}^{}$} =355(35) MHz, ΔT{5${\mathit{d}}^3$6s(a ${}_{}{}^5{}_{}{}^{}$F)6p ${}_{}{}^4{}_{}{}^{}\mathrm{D}_{3/2}^{\mathrm{o}}{}_{}{}^{}$–${5\mathrm{d}}^3$6s(a ${}_{}{}^5{}_{}{}^{}\mathrm{F}$)6p y ${}_{}{}^4{}_{}{}^{}\mathrm{D}_{1/2}^{\mathrm{o}}{}_{}{}^{}$}=-591(30) MHz, and ΔT{5${\mathit{d}}^2$6${\mathit{s}}^2$(a ${}_{}{}^3{}_{}{}^{}$P)6p ${}_{}{}^4{}_{}{}^{}\mathrm{P}_{3/2}^{\mathrm{o}}{}_{}{}^{}$–${5\mathrm{d}}^2$${6\mathrm{s}}^2$(a ${}_{}{}^3{}_{}{}^{}\mathrm{P}$)6p ${}_{}{}^4{}_{}{}^{}\mathrm{P}_{1/2}^{\mathrm{o}}{}_{}{}^{}$}=58(30) MHz, which are caused most probably by strong heretofore unknown perturbations.

• Received 5 April 1993

DOI:https://doi.org/10.1103/PhysRevA.49.120