Laboratory Measurement of CO2(ν2) + O Temperature-Dependent Vibrational Energy Transfer

The latest results from ongoing CO2(ν2)-O vibrational energy transfer measurements will be presented. The O + CO2 → O + CO2(ν2) vibrational uppumping process is a key contributor to 15-μm earthlimb emission and to upper atmospheric cooling in the 75-120 km altitude range. Model predictions of upper atmospheric density and temperature are sensitive to the assumed rate coefficient kO(ν2) for the relaxation of CO2(ν2) by O. Accurate accounting of kO(ν2) is necessary to derive the kinetic temperature and IR cooling rates from NASA TIMED/SABER radiometric data. In the present experiment, a 266-nm laser pulse photolyzes O3, producing O atoms and initiating a temperature jump, while transient diode laser absorption spectroscopy is used to monitor the time-dependent CO2(ν2) population. A vacuum-jacketed, liquid-nitrogen cooled reaction cell permits low-temperature measurements down to approximately 140 K. A second cell is used for high-temperature measurements up to about 550 K, spanning the range typically found in the mesosphere-lower thermosphere region. In new work, isotopically-labeled 13CO2 has been used to access lower temperatures and eliminate the deleterious effects of atmospheric absorption. Updated results and analysis will be presented.