The 3 snd 1 D to the 3 png 1 F Autoionization Resonances of Mg

Intense ultranarrow resonances have been observed in the photoionization of Mg from the singly-excited 3smd D (m=3,4,5,6) states to the doubly-excited 3png F (n=5,6,7) autoionization states using stepwise laser excitation and timeof-ßight mass spectrometry detection. The reported experimental energy resolution at an order of 10−7 of the photon energy represents a considerable improvement over the best in energy resolution to photon energy ratio of about 10−5 using the synchrotron radiation light source. The ultra-narrow 3png F resonances acquire a signiÞcant strength for the normally weak 3smd D → 3png F two-electron transition due to a strong conÞguration interaction with an overlapping broad 3pnd F autoionization series and the 3s2f F continuum. The measured line positions and transition widths are in close agreement with the theoretical results derived from a B-spline-based conÞguration interaction calculation.