Quantitative Relations in the Mass Spectra of n-Paraffins

The mass spectra of n‐paraffins in the C₆ to C₃₀ range have been examined for quantitative relations that must be predicted by any theory of ion formation by electron impact. An ion sum C(M, n) is defined as the sum of the normalized intensities of all ions of n carbon atoms from a n‐paraffin of M carbon atoms. The molar yield Y(M, n) per unit of ionizing current will be MC(M, n). It has been observed that for large ions from large molecules the yield is independent of M or n but proportional to (M—n). Yields for smaller ions, i.e., n between 3 and 15, are linear with M but not proportional to M. The yields in this region may be expressed as $${\mathrm{Y(M,n)=An}}^4{e}^{\mathrm{-bn}}{\mathrm{(M-n}}^{\prime })$$ where A and b are constants, one set applying for $\text{3≦n≦10}$ and another set applying for $\text{10≦n}$ ; the n′ values are constants, each depending upon the associated n. The observations indicate that the details of the fragmentation process for n‐paraffins depend primarily upon the type of molecular skeleton, i.e., straight chain, single valence carbon‐carbon linkages and secondarily upon the size of the molecule.