External-field shifts of the 199Hg+ optical frequency standard

Frequency shifts of the Hg-199(+) 5d(10)6s S-2(1/2) (F = 0, M-F = 0) to 5d(9)6s(2) D-2(5/2) (F = 2, M-F = 0) electric-quadrupole transition at 282 nm due to external fields ave calculated, based on a combination of measured atomic parameters and ab initio calculations. This transition is under investigation as an optical frequency standard. The perturbations calculated ave the quadratic Zeeman shift, the scalar and tensor quadratic Stark shifts, and the interaction between an external electric field gradient and the atomic quadrupole moment. The quadrupole shift is likely to be the most difficult to evaluate in a frequency standard and may have a magnitude of about 1 Hz for a single ion in a Paul trap.