Photodetachment of the [Formula Presented] ion at the [Formula Presented] threshold

A crossed laser-ion beam apparatus has been used to spectroscopically analyze electrons detached from an 80-keV beam of [Formula Presented] ions at a photon energy of 1.903 eV. At this energy only the [Formula Presented] photodetachment channel is open. The photon flux dependence and the angular dependence of the measured electron yield were used to determine the photodetachment cross section [Formula Presented] Mb and the asymmetry parameter [Formula Presented], respectively. The measured cross section is in significant disagreement with a recent R-matrix calculation. The present measurement has been used to establish an absolute scale for previous relative total cross-section data over a photon energy range 1.1–3.1 eV.