Construction and evaluation of an electron-ion coincidence apparatus using a large transmission coaxially symmetric mirror electron energy analyzer

We have developed an electron ion coincidence (EICO) apparatus using a coaxially symmetric mirror electron energy analyzer with a large transmission. The electron energy analyzer originally proposed by Kai Siegbahn in 1997 had a weak point that the performance is degraded by disturbance of the electric field near the end plates. We have improved this by adopting compensation electrodes. Simulation with SIMION 3D version 7.0 predicts that the energy resolution (FWHM) is E/ΔE=300 for a pointed beam and a solid angle of 1.2 sr. This value is about three times better than the predicted value for the cylindrical mirror analyzer (CMA) used in the previous EICO apparatus. The measured electron energy resolution is E/ΔE=120 for a beam size of 2 mm×1 mm, which is about 1.5 times better than that for the previous CMA. Auger electron photoion coincidence measurement of condensed H2O at 4a1←O 1s resonance showed that the measurement time required for a certain coincidence ion counts is reduced by one order of magnitude in comparison with the previous EICO.