We present a technique for measuring the radiative lifetimes of metastable states of negative ions that involves the use of a heavy-ion storage ring. The method has been applied to investigate the radiative decay of the np 3 2 P 1/2 levels of Te − ͑n =5͒ and Se − ͑n =4͒ and the 3p 3 2 D state of Si − for which the J =3/2 and 5/2 levels were unresolved. All of these states are metastable and decay primarily by emission of E2 and M1 radiation. Multi Configuration Dirac-Hartree-Fock calculations of rates for the transitions in Te − and Se − yielded lifetimes of 0.45 s and 4.7 s, respectively. The measured values agree well with these predicted values. In the case of the 2 D state of Si − , however, our measurement was only able to set a lower limit on the lifetime. The upper limit of the lifetime that can be measured with our apparatus is set by how long the ions can be stored in the ring, a limit determined by the rate of collisional detachment. Our lower limit of 1 min for the lifetime of the 2 D state is consistent with both the calculated lifetimes of 162 s for the 2 D 3/2 level and 27.3 h for the 2 D 5/2 level reported by O'Malley and Beck and 14.5 h and 12.5 h, respectively, from our Breit-Pauli calculations.

In recent years there have been many studies of multiple ionization of closed shell rare gas atoms by intense laser fields. Until now no similar work has been done in the study of more diverse targets such as negative ions where low binding energies and strong electron correlations could yield distinctive behaviour. We present the first results of ionization of more than one electron from a range of atomic negative ions by intense laser pulses. Although these pulses are long by modern standards, and tend to produce sequential ionization in atoms, the positive ion yields from the negative ions do not depend predictably on the ionization potentials. This suggests that there may, intriguingly, be an alternative mechanism enhancing double ionization at low intensities.

Single-, double-and triple-electron-impact detachments from the Cl Ϫ ion have been investigated over a collision energy range of 0-95 eV. The experiment was performed at the ion storage ring CRYRING at the Manne Siegbahn Laboratory. The Cl Ϫ ions, produced in a sputter ion source, were injected into the ring and accelerated to 2.7 MeV. Thereafter the ions were merged with an electron beam. The electrons served to cool the ion beam. Then they were used as a partner in the electron-ion collisions. The products of the detachment processes, Cl atoms, Cl ϩ , and Cl 2ϩ ions, were detected after the interaction region with surface-barrier detectors. The shapes of the cross sections for the single, double, and triple detachments show striking similarities.

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