Low-energy electron attachment to SF6 at sub-meV resolution using a tunable laser photoelectron method - art. no. 042706

Electron attachment to sulfur hexafluoride is studied using a photoelectron source of ultralow-energy electrons with sub-meV resolution. Vacuum-ultrav iolet laser radiation produced through nonlinear-optical techniques is used to photoionize xenon at and above its P-2(1/2)o ionization limit. The resu lting photoelectrons interact with sulfur hexafluoride admixed to the xenon . The electron energy is continuously scanned from 0 to 127 meV, with a res olution of 0.1 meV at threshold. Computational modeling indicates that the attachment cross section is well described by the Wigner threshold law at e lectron energies less than about 5 meV. Data at higher energies are best de scribed by the Wigner s-wave form, or by a Klots form with beta =0.228. Cus ps are observed at the omega (6), omega (1), and omega (3) vibrational mode s of SF6. While the omega (1) and omega (3) cusps have their maxima at the spectroscopic energies of 97.1 and 117.6 meV, respectively, the omega (6) c usp has its maximum at 46 meV, nearly 3 meV higher than its spectroscopic v alue of 43.2+/-0.4 meV. Possible explanations are considered, such as a low -l angular-momentum barrier, an overtone mode of SF6 excited by the collisi on, or clustering. The definitive cause of this shift is not understood.