Radiative decay spectra of selected doubly excited states in helium

Radiative decay spectra of doubly excited states in He have been measured after selective excitation with monochromatized synchrotron radiation. The decay spectra are in excellent agreement with predictions based on calculations.

Figure 1

Experimental geometry, $a=b=2\text{mm}$, $c=15\text{mm}$, the distance from the source to the spherical grating (shaded) is $d=235\text{mm}$, and the active area on the grating is $e\times f=70\times 30{\text{mm}}^2$. The grating is positioned in the direction of the polarization of the incoming radiation. After being diffracted at the grating the photons are detected by a multichannel plate detector positioned according to the Rowland condition.

Figure 2

(Color online) Experimental $n^{0,-,+}\to ml$ fluorescence spectra for $n=3–6$ (to $n=7$ for $n^{-}$ resonances), where the intense $3^0$ and $4^0$ scattering is measured with better energy resolution than the other emission spectra presented above. The energy positions of the most prominent final states are marked with vertical dashed lines. The data are shown on both linear (outer) and logarithmic (inner) intensity scales. The curves through the data points are the normalized theoretical predictions ${\sigma }^{{\omega }_i}\left(\omega \right)$ of the CRSB (solid line) and MCHF (dotted, red) models. The length and velocity form plots of the latter do not differ on these graphs.

Figure 3

(Color online) Partial $\left(\sim 38–42\text{eV}\right)$ FY spectra of $n^0,{\left(n+1\right)}^{-}$ doublets in experimental geometry which emphasizes ${{}^{1}D}_2$ final states. The data is compared with $\sigma \left({\omega }_0\right)$ of the CRSB (solid line) and of the MCHF model in the length form (dotted, red). The theory is scaled down to match the signal of the $n^0$ resonance. The MCHF result was shifted toward lower energy (see Table ).