Absolute frequency measurement of the 7s(2) S-1(0)-7s7 p P-1(1) transition in Ra-225

Transition frequencies were determined for transitions in Ra in an atomic beam and for reference lines in Te-2 molecules in a vapor cell. The absolute frequencies were calibrated against a GPS stabilized Rb clock by means of an optical frequency comb. The 7s(2) S-1(0)(F = 1/2)-7s7p P-1(1)(F = 3/2) transition in Ra-225 was determined to be 621 042 124(2) MHz. The measurements provide input for designing efficient and robust laser cooling of Ra atoms in preparation of a search for a permanent electric dipole moment in Ra isotopes.