Selective population of the [1s2s] 1S0 and [1s2s] 3S1 states of He-like uranium

The formation of the [1s2s] S states in heliumlike uranium (U90+) has been studied in relativistic collisions of initially lithiumlike uranium (U89+) ions with N-2 target molecules. By measuring projectile x-ray emission in coincidence with projectile ionization, a strong selectivity for the formation of the [1s2s] S states in heliumlike uranium is observed. This selectivity is found to be unaffected by the subsequent rearrangement of the atomic orbitals involved. By measuring the photon emission associated with the decay of the [1s2s] S-1(0) and the [1s2s] S-3(1) substates, we obtain for their relative population probabilities a ratio of close to 1. This finding deviates considerably from the assumption of a statistical distribution 2J+1.