Density-sensitive electric quadrupole decays in Ni-like ions observed in laser-produced plasmas

Abstract

The electric quadrupole transition 3${p}^{6}$3${d}^{10}$ ${\mathrm{}}^{1}$${S}_{0}$--3${p}^{5}$3${d}^{10}$4f (3/2, 7/1) J=2 has been observed in the spectra of Ta xlvi, W xlvii, Re xlviii, Pt li, Au lii, and Hg liii. The excited-level populations of Ni-like gold are calculated by means of a collisional-radiative model and show that the intensity ratio of the electric dipole 3${p}_{3/2}$-4${\mathrm{d}}_{5/2}$ and electric quadrupole 3${p}_{3/2}$-4${f}_{7/2}$ resonance transitions is sensitive to density in the range ${10}^{19}$--${10}^{21}$ ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}3}$, in qualitative agreement with the present observations.