Precision determination of the fine-structure splittings of the 5d and 6d states in potassium

The fine-structure splittings of the inverted 5 and 62D states of potassium were measured by observing level-crossing signals at high magnetic fields. The D levels were populated using step-wise excitations, employing two CW tunable dye lasers. For the fine-structure intervals delta W we find: delta W (5d) = -15,102.0 (5) MHz and delta W(6d) = -7,965.8 (6) MHz. These values are about 100 times more accurate than previous results for these states. An expression is given, describing the fine-structure splittings in the sequence of potassium 2D states. (orig.)