Observation of electric quadrupole decay in Xe45+ and Xe44+

Abstract

We have observed, for the first time in highly ionized atoms, electric quadrupole transitions between the $3p$ and $2p$ levels of fluorinelike and neonlike ${\mathrm{Xe}}^{45+}$ and ${\mathrm{Xe}}^{44+}$. We have made precision measurements ($\frac{\ensuremath{\lambda}}{\ensuremath{\Delta}\ensuremath{\lambda}}=2\ifmmode\times\else\texttimes\fi{}{10}^{4}$) of the relative wavelengths of the allowed electric dipole ($E1$) transitions and the forbidden electric quadrupole ($E2$) transitions connecting the $n=3$ and the $n=2$ levels. We have also derived from these measurements several $\ensuremath{\Delta}n=0$ intervals between states of opposite parity.