Spectrum of 13 CO 2 at 3420-3680 cm−1 (2.8 μm)

The 2.8 μm region is useful for the sounding of atmosphere pressure since it contains a number of weak and strong CO2 lines allowing a range of altitudes be sensed (1). This region has been selected for the measurement of pressure in the Halogen Occultation Experiment (HALOE, 2). To aid in the identification of spectral lines within this bandpass, we have recorded the absorption spectrum of 13CO2 in the laboratory. The data were obtained in the spectral interval 3420 to 3680 cm−1 with a vacuum grating spectrometer equipped with a 40 cm × 20 cm Harrison-ruled echelle and a 13C-enriched sample of carbon dioxide. The spectra were recorded both at room temperature and at 160°C. In the high temperature data, it was possible to observe transitions from high rotational levels and moderately high vibrational states. Measurements in this single spectral region provided information on 29 vibrational levels, 4 of which have been studied for the first time. Twenty-one bands have been identified, and about 80 percent of the 2000 lines recorded have been given assignments. The spectral resolution was about 0.03 cm−1.