Ionization and fundamental problems in gas analysis

Continuous change in the voltages applied to the electrodes in the separation syssem ( scanning ) gives rise to a relationship between the ion flow l-H and the atomic number which is proportional to the m/e ratio and expressed as  

This is the so-called mass spectrum, = r(M). The spectrum thus show/s the peaks i- as ordinates, plotted against the atomic number M along the abscissa. One of the difficulties in interpreting a mass spectrum such as this is due to the fact that one and the same mass as per the equation (4.2) may be associated w/ith various ions. Typical examples, among many others, are The atomic number M = 16 corresponds to CH and 0  

M = 28 for CO, and CjH Particular attention must therefore be paid to the follo A/ing points w/hen evaluating spectra  

1) In the case of isotopes we are dealing w/ith differing positron counts in the nucleus (mass) of the ion at identical nuclear charge numbers (gas type). Some values for relative isotope frequency are compiled in Table 4.2. 

3) Specific ionization of the various gases Sg j, this being the number of ions formed, per cm and mbar, by collisions with electrons this will vary from one type of gas to the next. For most gases the ion yield is greatest at an electron energy level between about 80 and 110 eV see Fig. 4.14. 

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