Clock and inter-combination line frequency separation in 171Yb

We have carried out concurrent optical frequency measurements of the (6s(2))S-1(0) - (6s6p)P-3(1) (F = 3/2) and (6s(2))S-1(0) - (6s6p)P-3(0) transitions in Yb-171, and in so doing have determined the frequency separation between the P-3(0) (F = 1/2) and P-3(1) (F = 3/2) levels with an uncertainty close to the ppb range. The knowledge of this frequency interval will aid experiments relying on the S-1(0) - P-3(0) line in Yb-171 and Yb-173 without access to highly accurate frequency standards.