Abstract: A quadrupole mass spectrometer was used to diagnose the ionic products from the microwave discharge through a mixture of air and water vapor. H3O＋,NO＋ and , important primary reagent ions in the chemical ionization mass spectrometry(SIFTMS) were observed at ionic beam current of up to 10 nA. The formation mechanisms for the above ions generated in the discharge were analyzed in conjunction with the ions detectied in the cases of N2, O2 and H2O microwave discharges, respectively. Thus, various ionmolecule reactions involving the primary ions , N＋, , O＋, H2O＋ and OH＋ were proposed to be responsible for the formation of H3O＋,NO＋ and , which were also demonstrated by computer simulation based on such ionmolecule reactions.

Key words: Ion source, Microwave discharge, Ion chemistry