Single and double photoionisation of Sr atoms between 38 and 50 nm

Photoionisation of atomic strontium has been investigated using a combination of a time-of-flight mass spectrometer and crossed beams of monochromatised synchrotron radiation and atomic strontium in the region of the Sr 4p-hole states. Relative cross sections for double and single photoionisation and the cross section ratio have been determined with a bandpass of 0.08 nm. With increasing photon energy, the ratio increases predominantly above some important 4p-hole states of Sr + due to opening of two-step autoionisation channels and finally reaches a value of more than 10. In the Sr 2+ yield spectrum, structure due to the Sr 4p 5 5s 2 ( 2 P 1 2/)nd series predominates, and the 6d to 9d members exhibit asymmetric Beutler-Fano autoionisation profiles. Detailed studies around the 4p-4d giant peak indicate the existence of double Auger processes by which Sr 2+ ions are formed from the Sr4p 5 5s 2 4d 1 P 1 state lying well below the lowest autoionising 4p-hole state of Sr + .