Photodetachment microscopy to an excited spectral term and the electron affinity of phosphorus

A beam of P- ions produced by a cesium sputtering ion source was photodetached in the presence of an electric field, with a single-mode ring dye laser. Neutral P can be produced at one or the other of the fine-structure sub-levels of its 3s23p3 2Do excited term. This is the first atomic photodetachment microscopy experiment with excitation of the parent neutral atom out of the fundamental spectral term. The background electron signal due to ground-state photodetachment notwithstanding, photodetachment microscopy images produced at the excited thresholds could be analysed to provide a measure of these excited-term thresholds with interferometric precision. Starting from the three possible fine-structure sub-levels of P- 3s23p4 3P, the five fine-structure thresholds that may be detected, taking the selection rules into account, have been measured. They are combined with the spectroscopic data available in the literature on neutral P to produce an improved experimental value of the electron affinity eA of phosphorus: 602 179(8) m -1 or 0.746 607(10) eV. Taking all covariances of the optimized energy levels into account, one can merge them with the former measure of the three lowest detachment thresholds of P-, which results in a slightly more precise value of eA(P): 602 181(8) m-1, or 0.746 609(9) eV. The accuracy of eA(P) is now essentially limited by the uncertainty on the 2Do 3/2 and 2Do 5/2 energy levels of the neutral atom. The fine-structure intervals of the 3s23p3 2D o doublet of the neutral atom and of the 3s23p4 3P triplet of the negative ion have their accuracy improved by more than one order of magnitude. © 2011 IOP Publishing Ltd.The authors wish to thank Evelyne Cottereau and Christophe Moreau, at the Laboratoire de mesure du carbone 14 (CEA Saclay), for making their expertise repeatedly available to us during the first months of operation of the SNICS II ion source, and Kevin Glize, for some useful numerical simulations that helped adapting the first decelerator to our low-energy beam requirement.Peer Reviewe