This was an experiment with the SAM calibration gas cell, which
contains approximately equal volumes of CO2, Ar, N2, and Xe with an
excess of 129Xe over terrestrial composition. The cell also contains
approximately 3.6 vol% fluorinated hydrocarbon compounds. The cell
composition is provided in Mahaffy et al., Space Science Reviews 170:
401-478, 2012.
The valve for the calibration cell was opened to the manifold for 0.02
sec to release gas into the manifold. A series of volume expansions
with intermediate pumping was performed to reduce gas pressure for QMS
analysis. Measurements were taken at manifold pressures of 2.4, 1.9,
and 0.7 mb. The gas was analyzed with the QMS, GC, and TLS.
The preliminary value provided for carbon isotope ratio of CO2 was
obtained from QMS data for m/z 45 and 46 by computing the average of
instantaneous isotope ratios throughout the first analytical region
at 2.4 mb.