High-charge-state formation following inner-shell photodetachment from ${\mathrm{S}}^{-}$

The formation of ${\mathrm{S}}^{+}$, ${\mathrm{S}}^{2+}$, ${\mathrm{S}}^{3+}$, and ${\mathrm{S}}^{4+}$ is observed following inner-shell photodetachment of ${\mathrm{S}}^{-}$. The photodetachment spectra for all possible ionic products are obtained over a large region of photon energies covering both the $2p$ and $2s$ thresholds (${\mathrm{S}}^{5+}$, is energetically allowed at the higher photon energies, but not observed), and are placed on an absolute scale. The $2s$ threshold energy is measured to be 224.6(5) eV, allowing the determination of the neutral atomic S $2s^{-1}3s^{2}3p^5$ inner-shell excited state energy for the first time. The ${\mathrm{S}}^{-}2s^{-1}3s^{2}3p^6{}^2\mathrm{S}_{1∕2}$ state is observed as a Feshbach resonance 2.3(5) eV below the $2s$ threshold in the ${\mathrm{S}}^{+}$, ${\mathrm{S}}^{2+}$, and ${\mathrm{S}}^{3+}$ product channels.

Figure 1

(Color online) Observed ${\mathrm{S}}^{+}$ (◯), ${\mathrm{S}}^{2+}$ (+), ${\mathrm{S}}^{3+}$ (▵), and ${\mathrm{S}}^{4+}$ (◻) production following photoabsorption in ${\mathrm{S}}^{-}$, scaled to measured absolute cross sections (filled circles, see Table II). For presentation purposes, ${\mathrm{S}}^{3+}$ and ${\mathrm{S}}^{4+}$ signals have been magnified by a factor of 3 and 50, respectively.

Figure 2

(Color online) Signal observed from ${\mathrm{S}}^{+}$ (◯, left inner scale), ${\mathrm{S}}^{2+}$ (+, left outer scale), and ${\mathrm{S}}^{3+}$ (▵, right scale) near the $2p$ threshold. Over this range, the signals from all channels have nearly identical shapes. The curves are Wigner s-wave threshold laws (${\epsilon }_t=161.04\left(6\right)\mathrm{eV}$, see Ref. 6).

Figure 3

Possible negative ion resonance in the ${\mathrm{S}}^{+}$ channel (extracted from Fig. 1 data, see text). The curve is a Lorentzian fit to the data above 170 eV. The Lorentzian is clearly truncated by the threshold, but otherwise fits the data well.

Figure 4

(Color online) Observed ${\mathrm{S}}^{+}$ (◯, top left scale), ${\mathrm{S}}^{2+}$ ($+$, right scale), and ${\mathrm{S}}^{3+}$ (▵, bottom left scale) production following photodetachment near the $2s$ threshold. The data were taken at $0.7\left({\mathrm{S}}^{+}\right)$ and $0.3\mathrm{eV}({\mathrm{S}}^{2+},{\mathrm{S}}^{3+})$ spectral resolution. The $2s\to 3p$ Feshbach resonance is observed near 222 eV, just below the $2s$ threshold. The solid curves are a Fano profile plus $p$-wave Wigner law. Also shown are the noninterfering continuum background (dotted lines) and the Fano component extended to higher energies (dashed curves).