High-resolution photodetachment spectroscopy from the lowest threshold of ${\mathrm{O}}^{-}$

We conducted photodetachment spectroscopy near the lowest detachment threshold from ${\mathrm{O}}^{-}$ in a 1-T field with sufficient resolution to observe a magnetic field structure similar to that observed in experiments conducted at the threshold of the electron affinity. These observations included not only cyclotron structure but also, to a smaller degree, individual Zeeman thresholds. The experiment was conducted in a Penning ion trap and with a single-mode, tunable, amplified diode laser. Finally, analysis of our results yielded a measurement of the lowest threshold energy.

Figure 1

Schematic diagram of the major optical apparatus and the ion trap. The ions undergo photodetachment with light from a tunable, single-mode, amplified diode laser. A computer-controlled mechanical shutter maintains a constant optical flux, measured by the photodiode, from cycle to cycle of the data acquisition.

Figure 2

Photodetachment data at the ${}^2{P}_{1/2}\to {}^3{P}_2$ threshold of ${\mathrm{O}}^{-}$. The percent of ions surviving laser illumination is plotted as a function of photon energy. The data shown are for a field of 1.36 T and $\pi$-polarized light. The solid curve shows a fit to the data, from which is derived a measure of the field-free detachment threshold. Labeled arrows show the expected locations of the Zeeman transitions as indicated in Table .

Figure 3

Photodetachment data at the ${}^2{P}_{1/2}\to {}^3{P}_2$ threshold taken at higher energy resolution, with $B=1.36$ T and using $\Delta E({}^2{P}_{1/2}\to {}^3{P}_2$-polarized light. The solid curve shows a fit to the data, and the labeled arrows show the locations of the expected Zeeman thresholds.