Eiler, John

Reviews by Fran9ois Robert, John Eiler, John Valley, and Mark Thiemens improved the manuscript and are gratefully acknowledged. Helpful discussions of all things isotopic with colleagues too numerous to mention are also valued and appreciated. NASA grants for support of the work discussed herein are acknowledged by both authors. 

Normal gas-source mass spectrometers do not allow meaningful abundance measurements of these very rare species. However, if some demands on high abundance sensitivity, high precision, and high mass resolving power are met, John EUer and his group (e.g., Eiler and Schauble 2004 Affek and Eiler 2006 EUer 2007) have reported precise (<0. l%c) measurements of CO2 with mass 47 (A47-values) with an especially modified, but normal gas-source mass spectrometer. A47-values are defined as %o difference between the measured abundance of all molecules with mass 47 relative to the abundance of 47, expected for the stochastic distribution. 

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