Ds. Mcgrew et al., CONCENTRATION ENRICHMENT IN THE ION-SOURCE OF A PULSED ELECTRON-BEAM HIGH-PRESSURE MASS-SPECTROMETER, International journal of mass spectrometry and ion processes, 139, 1994, pp. 47-58
Citations number
12
Categorie Soggetti
Spectroscopy,"Physics, Atomic, Molecular & Chemical
The magnitude of concentration enrichment of methyl iodide in methane,
helium, and argon buffer gases within the ion source of a pulsed e-be
am high pressure mass spectrometer (PHPMS) is characterized here by a
theoretical model and by kinetic measurements of the gas phase ion/mol
ecule reaction, F- + CH3I --> CH3F + I-, at 150-degrees-C. A relativel
y simple PHPMS ion source is used in which the magnitude of enrichment
is related only to the ventilation of individual molecules out of the
ion source by passage through its ion exit and electron entrance slit
s. It is shown that significant enrichment does occur under typical op
erating conditions of this source and that the magnitude of enrichment
is strongly dependent on the choice of ion source pressure. These obs
ervations are explained in terms of the flow conditions thought to exi
st in the ion source. Recommendations for improving the accuracy of fu
ture kinetic and equilibrium measurements by the PHPMS are provided.