Recent experimental achievements with negative ions

Experimental results obtained about the atomic physics of negative ions since the Physica Scripta 1991 review are presented. Most new data concern the metastable states and resonances of He and alkaline-earth negative ions, and the ions of the C column. A few photodetachment experiments were also performed on ions submitted to external fields, and we have now a better understanding of the response of negative ions to microwaves and ponderomotive threshold shifting. A great progress was made in the study of multiphoton detachment processes; 1991 was the year of discovery of excess-photon detachment. Every year brings new precision detachment threshold measurements about, but still relying on the 1985 measurement numerical reasons make it necessary to revise the electron affinity of oxygen: EA(O) = 11 784.648(6)cm¹, or 1.4 611 107(17)eV.