The electron-stimulated desorption ions from the ionizer of a quadrupole mass spectrometer

The species and the pressure dependence of the electron-stimulated desorption (ESD) ions from the grid surface of the ionizer of the quadrupole mass spectrometer were measured by the QMS with the Bessel-box-type energy analyzer (BB-QMS). The BB-QMS was developed in order to measure true mass spectra of gas phase without ESD ion effect in high to extreme high vacuum. The ESD ions observed in typical residual gasses such as water, carbon monooxide, oxygen and carbon dioxide were H+ (H2O), O+ (H2O, CO, O2, CO2), OH+ (H2O). The intensity of the ESD ion signals showed saturation upon increasing coverage of the water molecules on the grid surface.