2-PHOTON DECAY OF 2 S-1(0) AND 2 S-3(1) STATES OF HELIUM-LIKE IONS

Systematic calculations of two-photon decay rates of metastable 2(1)S( 0) and 2(3)S(1) states are presented for heliumlike ions with nuclear charges in the range Z = 2-100. These calculations include retardation and are carried out using relativistic configuration-interaction wave functions that account for the Breit interaction. Photon energy distr ibutions and total rates are given. The relativistic 2(1)S(0) decay ra tes agree, to within two standard deviations, with precise measurement s for heliumlike Ar, Ni, Br, Kr, and Nb. The calculated 2(1)S(0) rates are 30% smaller than the corresponding nonrelativistic rates at high Z. The 2(3)S(1) two-photon decay rates remain a factor of about 10(-4) of the corresponding M1 rates throughout the helium isoelectronic seq uence.