A mid-infrared wave-number range has been identified as being useful for laser measurements of CO and CO2 gases that contain various combinations of isotopes of C and O. The isotopic species are 12C16O (common CO), 13C16O, 12C18O, 16O12C18O,12C16O2 (common CO2), and 13C16O2.
More specifically, the wave-number range from about 2,036.2 to 2,038.4 cm-1(wavelength range from about 4.9111 to about 4.9058 µm) contains two absorption spectral lines for 12C16O2, a group of lines for 13C16O2, and one line for each of the other isotopic species (see figure). The range is narrow enough that it can be spanned by a typical tunable laser.
From measurements of the absorption of laser light in this wavelength range, one can determine simultaneously the temperature of a gas mixture and the concentration of each of the six isotopic species. Potential applications for instruments based on this measurement principle include Earth and planetary gas spectrometers; analysis of exhaled, isotope-tagged CO and CO2 for medical diagnosis; analysis of isotope-tagged CO and CO2 for research on the operation of automotive engines and the resulting pollution; and other applications in industries that involve the sensing and/or measurement of gases.
This work was done by Christopher Webster of Caltech forNASA's Jet Propulsion Laboratory.