Species mass scattering efficiencies

Statistical Estimation of Species Mass Scattering Efficiencies... 

Selection of the neutral species for use in a reaction/collision cell mass spectrometer is a balancing act between many competing factors. First, the neutral must be amenable to introduction into the cell in a convenient, controlled and reproducible manner. Also, the neutral must have a relatively low atomic or molecular mass so as to reduce the effects of collisional scattering. Lastly, the neutral must react with the interference ion with a high efficiency per collision to effect rapid and quantitative conversion (preferably to a single product). 

The detector, which usually can be rotated to various scattering angles, must be able to differentiate among the species present. Surface-ionization detectors with efficiencies of approximately 10% are employed for reactions of metal atoms yielding metal halide products. Laser-induced fluorescence has proved to be an excellent detector for group Ilb halides and a few other systems. In general, products can be detected by electron-bombardment ionization with subsequent analysis by a mass spectrometer. Unfortunately, these mass spectrometer or universal detectors have a low detection efficiency ( 0.1%,) thus, beam machines with such detectors require several differentially pumped chambers to reduce the background pressure (of the mass of interest) in the detector to torr. Modulation tech-... 

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