Effect of Evaporative Cooling on Photodetachment from O^- at the ²P_3/2 → ³P₂ Threshold

The ²P_3/2 → ³P₂ photodetachment threshold for ions such as S^- and O^- has been examined in numerous experiments conducted near the electron affinity. Our most recent experiment explores the effect of evaporative cooling on the spectroscopy of O^- at this threshold, as a function of photon energy in the range of 11784 -11788 cm^-1. The apparatus used was a Penning ion trap which traps and stores the ions, and a tunable, amplified diode laser. Comparing the photodetachment spectrum with and without cooling shows more distinct structure with lower temperatures. The more defined structure may be due to diminished average kinetic energy which decreases the thermal broadening.