(project supervisor) Phone: +49 (0)6159 71 2125 E-Mail: d.winters(at)gsi.de or Prof. Dr. Thomas Stöhlker (PhD supervisor) Phone: +49 (0)6159 71 2722 E-Mail: t.stoehlker(at)gsi.de [...] because their first excited state, i.e. the (1s 2 2s2p) 3 P 0 , has an almost infinite lifetime in the absence of nuclear spin ( I ), as it can only decay by a two-photon E1M1 transition to the (1s 2 2s 2 ) [...] in Darmstadt. In such an experiment, the energy splitting can be obtained with very good accuracy, i.e. of the order of ~10 -5 , and be compared with recent calculations. In April 2010 we successfully applied