Observation of Penning electron detachment by electronically excited potassium atoms in high Rydberg states

Penning electron detachment is a process in which an electronically excited neutral species collides with an anion and detaches an electron from it by transferring its excitation energy, viz., A- + N* → A + N + e-. While there have been theoretical studies relating to the mechanism of Penning detachment, there have been few experimental investigations of this fundamental process. In this work, Penning electron detachment of sulfur pentafluoride anions by potassium atoms, which had been selectively excited to high Rydberg electronic states, was investigated by directly observing its occurrence via the depletion of the SF5- anion signal in mass spectra, viz., SF5- + K** → SF5 + K + e-. Scanning the excited states of potassium in the range of 8d-32d and 10s-33s (excitation energy 4.11-4.33 eV) showed a significant dependence of the Penning detachment cross section on the excitation energy of potassium. Combining quantitative Penning detachment results with the electron affinity of SF5 (4.4 eV), which we had determined using anion photoelectron spectroscopy, demonstrated that Penning detachment occurred when the total available energy, that is, the SF5- + K** collision energy + the K** excitation energy, exceeded the electron affinity of SF5.