Highly correlated electronic bounding and spin effect: confirmation of an autodetaching state of O$^-$

Abstract

The existence of an auto-detaching state of O$^-$ with a lifetime on the scale of a hundred nanoseconds is demonstrated both experimentally and theoretically. The O$^-$ lifetime values are determined using two recently developed methods. The experimental approach is based on a derivation from measured electron-loss cross sections combined with time-of-flight spectrometry. For the theoretical approach, the continued Green's function within the formalism of Fano-Feshbach is applied. We present the measured lifetime value of $100 \pm 10 \text{ ns}$. The calculated lifetime value is 75 ns, and is associated with the (2p$^3$3s$^2$)$^4$S state of O$^-$. We discuss how the existence of a 100-ns-lifetime oxygen metastable anion can impact the modeling of oxygen-containing systems.

Figures (7)

• Figure 1: Schematic diagram of the apparatus. Not to scale.
• Figure 2: Examples of the measured data at 2.5 keV. Relevant reduced signals of the SGR and BAT methods as a function of the target thickness. The top panel corresponds to SGR method and the lower panel corresponds to the BAT method. The electron detachment cross-section is given, at first order, by the slope for each curve.
• Figure 3: Present results for the measurements of the collision-induced total electron loss cross sections (CS) for the interaction system: O$^-$ + O$_2$. Measured with BAT method (open squares) were derived from experimental parameters in Eq. (\ref{['eqF-1']}). Measured with SGR method (closed squares) were derived from Eq. (\ref{['eqF0']}).
• Figure 4: Partial compilation of electron loss cross sections for the interaction system: O$^-$ + O$_2$ from relevant authors. Present results: BAT ($^b\sigma$), SGR ($^s\sigma$). Bailey & Mahadevan bailey1970, Hasted & Smith hasted1956, Bennet et al.bennet1975. Ranjan & Goodyear ranjan1973, Comer & Shulz comer1974, Mauer & Shulz mauer1973. Electron transfer cross sections: Mathis & Snow mathis1974 Roche & Goodyear roche1969, Rutherford & Turner rutherford1967.
• Figure 5: Auto-detaching CS, $^m\sigma$, of the metastable population as a function of the time of flight derived according to Eq. (\ref{['betapar']}) for the interaction system O$^-$ + O$_2$$\rightarrow$ O$^*$ + e$^-$ + O$^*_2$. The dashed line represents a minimum square fit to an exponential decay from which a value of $107 \pm 15 \text{ ns}$ for $\tau$ was derived. The error bars represent total uncertainty: the error from the AEF edge effects and the average standard deviation from the numerical fit.