A Computer Program for the Prediction of Mass Spectrum Isotope Peaks Molecular formulas are commonly assigned or confirmed by the determination of the exact molecular weight of the parent ion utilizing high-resolution mass spectroscopy. Although it is a powerful technique, this method is often not readily available. The use of isotope peak intensities is also an adequate and u e f u l technique for confirmation of molecular formulas, and requires only Lowresolution mass spectra. This method may he used for nearly all compounds for which mass spectra can be obtained, and is particularly effective when the compound in question contains one or more elements having several isotopes of fairly large natural abundance. Complex parent peak clusters are often observed for these compounds, and comparison with the predicted pattern makes positive assignment of the molecular formula pnssible. In our work with orgenosilicon-germanium and organogermanium compoun&,',Z it was desired to cillculate the theoretical relative intensities for the mass spectrum parent peaks of certain compounds (for example, dodecamethyl438 438 trigermacyclohexasilsne, MedirGea), in order to determine unequivoctllly the molecular formulas of the particular compounds. Similar computations would obsrnd also be very helpful in determining the identity of fragment ions present in the u~.1.d mass spectra. In order to facilitate our calculations, we designed a computer program in Fortran IV for the IBM 1130. This program calculates the theoretical values for the relative intensities of the mass spectrum peaks for compounds containing m y number of and any combination of the elements carbon, hydrogen, oxygen, nitrogen, sulfur, silicon, and germanium. In addition, other elements can he easily added to the program. Thus it is useful for virtually all organic compounds as well as many main group organometallic species. A polynomial of the form (A)'(B)-(CP.. .is evaluated to determine the ahundances of all possible combinations of isotopes (where each capital letter represents the sum of the relative tlbundances of the isotopes of each individual element involved and where each exponent is the number of stom of that particular element found in the molecule). The ahundances due to combinations of isotopes which add up to the same nominal molecular weight are combined, and the relative peak intensities are printed out. A "stick plot'' of the parent region is also printed. An example of the printed plot is shown in the figure for the compound dodecamethyl-1,4digermacyclohexasilhne. The agreement with the observed spectrum in the parent peak region is excellent. A listine of the oroeram will he sent to all interested readers uoon reauest.
Volume 48, Number 1 1, November 1971
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