Measurement of the electron affinity of As and the fine structure of As− using infrared threshold photodetachment spectroscopy

The negative ion As- has been investigated using infrared threshold photodetachment spectroscopy. The relative cross section for neutral atom production was measured with a crossed OPO-ion beam apparatus over selected photon energy ranges between 0.63 – 0.82 eV. s-wave thresholds were observed for detachment from As-(4p4 3P0,1,2) to the As (4p3 4S3/2) ground state. The measurements yield preliminary values for the electron affinity of As (0.8048(2)) eV) and the fine structure intervals of As- (0.1276(2) eV for 3P1 – 3P2 and 0.1643(10) eV for 3P0 – 3P2). The present results substantially reduce the uncertainties in these quantities.