Stark spectroscopy of the 6s5d1D2 – 5d2 1D2 forbidden transition in atomic barium

We report an observation of the 6 s 5 d 1 D 2 – 5 d 2 1 D 2 forbidden transition in Ba atom by means of high-resolution atomic-beam laser spectroscopy. Stark shifts and splittings of this forbidden transition were measured for 136 Ba and 138 Ba using the Stark-induced interference method, increasing as the applied electric field increases. From measured spectra at various electric fields, scalar and tensor polarizabilities of the forbidden transition were obtained and found to be much larger than those of other levels. The forbidden transition with large electric polarizabilities, resulting from strong mixing between the two closely lying levels of 5 d 2 1 D 2 and 5 d 6 p 1 D 2 , provides a good candidate for atomic parity non-conservation study.