Generation of negative ions in the gas phase from a 12CaO⋅7Al2O3 membrane-coated ceramic heater under atmospheric pressure

12 CaO ⋅ 7 Al 2 O 3 (C12A7) crystal is able to generate strong and high purity oxygen anion (O−) beam under reduced pressure. However, the emission of O− or related species under atmospheric pressure has not been evaluated. In this study, the characteristics of negative ion species emissions from the C12A7 membrane-coated ceramic heater under atmospheric pressure were investigated by quadrupole mass spectrometer. Negative ion species were confirmed to be emitted even under atmospheric pressure. It was supposed that the detected negative ion clusters, such as O−(H2O)n, O2−(H2O)n, and CO4−(H2O)n, were generated by the reaction of negative ions emitted from the heater with impurities in He gas.