Experimental lifetime of the metastable 5D 3/2 state in Ba+

A discrepancy exists between theoretical and experimental lifetimes of the metastable 5D _3/2 state in Ba⁺. In order to redertermine that lifetime, we probe the population of the metastable 5D _3/2 state of a Ba⁺ ion cloud stored in a Paul ion trap in the presence of He buffer gas as the function of time delay after pulsed laser excitation of this state. The measured decay rates at different buffer gas pressures are extrapolated to zero pressure and we obtain a radiative decay time of 48.0±5.9 s. This is not in agreement with theoretical predictions of about 80 s, but reduces the discrepancy from a previously reportet experimental value of 17.5 s. If the possibility of finestructure mixing to an adjacent 5D _5/2 level by collisions is considered our value represents a lower limit of the radiative lifetime for the 5D _3/2 state.