Relativistic coupled-cluster theory of quadrupole moments and hyperfine structure constants of 5d states in Ba+

The narrow optical frequency resonances of the 6s S-2(1/2)-> 5d D-2(3/2) and 6s S-2(1/2)-> 5d D-2(5/2) forbidden transitions in Ba+ have been proposed as suitable frequencies for a new optical frequency standard. The major sources of errors in measurements of singly ionized systems are due to the quadratic Zeeman and electric quadrupole shifts. We report here the most accurate calculations to date for the hyperfine structure constants and electric-quadrupole moments of the 5d D-2(3/2) and 5d D-2(5/2) states in Ba+, which determine the quadratic Zeeman and electric quadrupole shifts. Relativistic coupled-cluster theory has been employed to calculate these quantities and large electron correlation effects are observed. It is also shown that for the high accuracy calculation of the 5d D-2(5/2) state in Ba+, all order core polarization effects play a significant role.