Measurement of the 1s2s S-1(0)-1s2p P-3(0,1) transitions in heliumlike nitrogen by fast-beam laser spectroscopy

For a large range of Z the intercombination 1s2s S-1(0) - 1s2p P-3(1) interval in heliumlike ions is accessible to spectroscopy with infra-red lasers. Using a CO2 laser and a nitrogen ion beam from a Van de Graaff accelerator, together with careful energy calibration, we obtained 986.321(7) cm(-1) for the N5+, 2(1)S(0)-2(3)P(1) transition. This result is a severe test of two-electron Lamb Shift calculations. In N-14(5+) there is also sufficient hyperfine mixing of the 2(3)P(0) and 2(3)P(1) levers to permit spectroscopy of the otherwise totally forbidden 2(1)S(0)-2(3)P(0) interval. By careful choice of CO2 laser line it was possible to observe the 2(1)S(0)-2(3)P(0) and the 2(1)S(0)-2(3)P(1,F=2) transitions at similar ion beam energies, yielding a precise result for the 2(3)P(1)-2(3)P(0) fine-structure interval of 8.6709(10) cm(-1). This result provides a test of current calculations of QED contributions of order alpha(7)m(e)c(2), which are required for obtaining a new value of the finestructure constant from the finestructure of helium.