High Resolution, Temperature Dependent Photoabsorption Cross Section Measurements of O₂ and N₂ Important to the Earth's Atmosphere

Principal Investigator (JPL):	Joseph Ajello
Co-Investigator (JPL):	Isik Kanik
Co-Investigator (SwRI):	Richard Link

To answer the need for accurate photoabsorption cross sections in modeling satellite UV albedo observations of the Earth, we have established a laboratory UV spectroscopy program at the Jet Propulsion Laboratory (JPL). As part of this program, we proposed to measure the cross sections of the important absorbers, N₂ and O₂, present in the lower thermosphere of the Earth at a resolution up to 0.0008 nm and at the temperature of the absorbing layer ( 200 - 1000 K). These two species most severely affect the atmospheric transmission of EUV resonance radiation due to their complex structure from Rydberg states that converge to the ground and excited states of the molecular ion. Atomic O is also present in the thermosphere in great abundance but has a smooth ionization continuum in this spectral region (Link et al., 1994).

Recent Developments:

We have measured the photoabsorption cross section for O₂ at the OI resonance triplet lines 1302, 1304, and 1306 Å from 295 - 573 K with absolute uncertainties of ± 1-3% over the range of temperatures and pressures measured (Ahmed et al., 1996).

We have just completed temperature-dependent photoabsorption measurements for O₂ at the NI 1200 Å, 1492 Å, and 1742 Å lines. The results have been submitted for publication (Kanik et al., 1997).

For further information, e-mail: help15@swri.edu
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