Coincidence measurement of energy-selected electrons and mass-selected ions (electron-ion coincidence (EICO) spectroscopy) is a powerful technique to clarify ion desorption mechanism induced by electron transitions, because excited states leading to ion desorption is directly identified. Information on the coincidence ions, however, is limited to the mass and the yield so far. In order to obtain information on kinetic energy and desorption polar angle of ions, we have developed a new polar-angle-resolved miniature time-of-flight ion mass spectrometer (TOF-MS), which can be used for EICO spectroscopy. The TOF-MS consists of a shield for electric field, an ion drift electrode with three meshes, and microchannel plates with three concentric anodes. By using SIMION 3D version 7.0 we simulated ion trajectories of H+ for the TOF-MS with a drift bias of -30 V. The results show that the desorption angles of H+ with a kinetic energy of 3 eV detected by the innermost anode, the intermediate anode, and the outermost anode are 0°17°, 22°48°, and 57°90°, respectively. The performance of the TOF-MS was evaluated by measuring H+ yield spectra and Auger electron-H+coincidence spectra of condensed water (H2O).
