Meinschein ct al. : Evidence in Meteorites of Former Life 567 



Large peaks may appear at masses equal to those of molecules, fragments 

 containing stable ring systems, or fragments of different structure and common 

 mass. w-Parafiftns and polycycloalkanes form more molecular or "parent" ions 

 than do branched chain parat^ins or monocycloalkanes. FVagments containing 

 the stable, partially hydrogenated phenanthrene ring system frequently give 

 large peaks. Isoprenoids usually have a number of methyl branches or substit- 

 uents, and several different fragments of the same mass can be formed when 

 an isoprenoid loses a methyl group. Common mass ions of isoprenoids, also, 

 yield large peaks in the mass spectra of naturally occurring saturated hydro- 

 carbons. 



"Parent," stable ring, or common mass ions can be identitied in most cases. 

 For convenience, the whole number atomic masses of C = 12 and H = 1 are 

 used in calculations of ion mass numbers, and fragment ions generally have odd 

 mass numbers. Therefore, stable ring and common mass ions are found 

 predominantly in odd numbered .v columns. All "parent" ions of hydrocarbons 

 have even mass numbers, and these ions appear in even numbered .v columns. 

 Common mass ions normally appear a row above and one column to the left of 

 "parent" ions; whereas most stable ring fragment ions have masses 50 or more 

 units less than the masses of the molecular ions. Thus, stable ring ions appear 

 chietly in odd .v columns several rows above the "parent" ion region. 



Some stable ring ions, however, are formed by breaking 2 bonds. These 

 ions have even mass numbers. An example of an even mass stable ring ion is 

 the -v = —6 and C^ = 16, mass 218, ion in the cholestane'*^ mass spectrum. 

 The even mass numbers of some fragment ions lead to ambiguity in the identi- 

 fication of "parent" ions. This ambiguity can be removed in many cases by 

 additional fractionations or by information gathered from the mass spectra 

 of reference compounds. Studies of thousands of mass spectra of saturated 

 hydrocarbon mixtures from plant and animal lipids, sedimental extracts, and 

 crude oils have shown that certain fragment and "parent" ions commonly 

 yield large peaks at particular masses. Some of these large peaks may be 

 absent in the mass spectra of highly paraffinic fractions, but further separations 

 usually yield cycloalkyl concentrates in which these large peaks appear as they 

 do in most biological and sedimental hydrocarbons. 



The peaks that are normally large in the spectra of naturally occurring 

 saturated hydrocarbon mixtures have been mentioned in previous publica- 

 tions,^^"^^ and many of these peaks will be indicated, again, in the subsequent 

 interpretation of the meteoritic hydrocarbon spectra. But, it is noteworthy 

 in the spectra of cholestane^^ that the .v = — 7, C ^ = 26 (common mass ion) 

 and 17 (stable ring ion); x = —6, C ;i^ = 27 ("parent" ion) and 16 (stable 

 ring ion) ; and .r = — 5, C ^ = 11 (stable ring ion) peaks are large. These same 

 mass peaks have been observed to be large in either total or refined saturated 

 hydrocarbon fractions which have been isolated from extracts of terrestrial 

 sediments. Peaks at x = —6, C# = 28, 29, and/or 30, which may be 

 ''parent" ions of compounds structurally related to parent sterol hydrocarbons 

 other than cholestane, are also prominent in most naturally occurring alkane 

 fractions. 



Mass spectra of the meteoritic hydrocarbons presented in tables 6 and 8 



