Steady-state models of stable isotopic distribution
. Isotopes in Environmental and Health Studies, 39: 219-232.
The natural gas form Xushen-1 in Songliao Basin exhibited a heavier [[delta].sup.13][C.sup.1] value (-29.40[per thousand]) than other natural gases and was characterized by a reversed carbon isotopic distribution
pattern ([[delta].sup.13][C.sup.1] > [[delta].sup.13][C.sup.2] > [[delta].sup.13][C.sup.3] > [[delta].sup.13][C.sup.4] > [[delta].sup.13][C.sup.5]), which suggested that it is an abiogenic gas .
The molecule's average mass was slightly higher than the exact mass due to the isotopic distribution
, giving an M+1 ion one amu higher.
Industrially produced carbon dioxide has a different isotopic distribution
to that of atmospheric air, which measurement instruments read differently.
Monoisotopic mass is preferred for comparison because it is not subject to this uncertainty and because it does not depend on the characteristics of the isotopic distribution
, which varies with mass.
This isotopic distribution
results from kinetic fractionation effects whereby alkyl groups separating from source organic matter cleave preferentially at the weaker [C.sup.12]-[C.sup.12] rather than [C.sup.12]-[C.sup.13] bonds (3).
Lead recycling notwithstanding, there are still measurable deviations from co-linearity in the lead isotopic distribution
of the minor ratios (vs.