M1 and E2 decay-dependent lifetime of the lowest 1S0 level in C-like ions up to Ne4+ measured at a heavy-ion storage ring

Electric-dipole forbidden transitions within the ground configuration of many ion species play an important role in the diagnostics of terrestrial and astrophysical plasmas, and knowing their rates is essential for collisional-radiative models and spectral simulation. The dominant decay channel of the 2s22p2 1S0 level in the ground configuration of C-like ions changes from electric quadrupole to magnetic dipole within the first few ions of the isoelectronic sequence. Using an electron cyclotron resonance ion source at the TSR heavy-ion storage ring, we realize a lifetime measurement on the system Ne4+ where the magnetic dipole decay channel becomes dominant. These data complement our earlier storage ring lifetime measurements on N+, O2+ and F3+, which we discuss together with the present new result and the available theoretical calculations in their isoelectronic context. (paper)