Physics
Scientific paper
May 2002
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2002agusmsa32a..15a&link_type=abstract
American Geophysical Union, Spring Meeting 2002, abstract #SA32A-15
Physics
0310 Airglow And Aurora, 0342 Middle Atmosphere: Energy Deposition, 0358 Thermosphere: Energy Deposition, 0394 Instruments And Techniques, 0399 General Or Miscellaneous
Scientific paper
Emission from high vibrational levels of two of the three lowest singlet states of O2 (b and {c}) has been detected in the Earth's nightglow. The vibrational population distribution of the {b} state was found to extend to levels up to υ = 15 whereas the {c} state is present in levels υ = 7 to 11.1,2 Three-body recombination of O atoms is the major source of these high vibrational levels in the upper atmosphere. These levels can be formed either directly in the recombination event or by subsequent collisional relaxation. Little or no information exists on the relaxation pathways and the relevant kinetic parameters. This knowledge is essential in order to model the terrestrial nightglow. Even at the high altitude of the emitting layer, collisional processes control the fate of excited O2. In this work, we expand our previous studies on O2(a, {b}, and {c})3 to include more vibrational levels, different colliders, and temperatures between 150 and 300 K. In our two-laser experiments, ground-state O2 molecules are excited to a selected vibrational level of the O2({A} or {c}) states with the first laser pulse. A second pulse ionizes the electronically excited O2 molecules via resonantly enhanced multi-photon ionization (REMPI). The temporal evolution of the vibrational population is obtained by varying the time delay between the two pulses. For the {c} state at 155 K, the collisional removal rate constants in O2 are (2.6 +/- 0.3) x 10-11 and (7 +/- 3) x 10-11 cm3s-1 for υ = 10 and 11, respectively. As the temperature is varied between 155 and 300 K, little or no change is observed in the magnitude of these rate constants. In contrast, the rate for υ = 9 increases by more than a factor of 3 in the same temperature range. The removal of O2({b}, υ = 15) by O2 has a rate constant of (2.7 +/- 0.3) x 10-12 cm3s-1 at 155 K and is approximately 5 times slower than that of O2({a}, υ = 19). Preliminary results indicate that O2({a}, υ = 19) is removed 20 times faster than υ = 18. Overall, the collisional removal rate constants and their temperature dependence vary markedly with the initial electronic state, the vibrational level, and the identity of the collider gas. Experiments are currently in progress to determine the relevant relaxation pathways and energy transfer mechanisms. This work is supported by the NASA Ionospheric, Thermospheric, and Mesospheric Physics, Supporting Research & Technology, and the Planetary Atmospheres Programs. 1. T. G. Slanger, P. C. Cosby, D. L. Huestis, and D. E. Osterbrock, J. Geophys. Res., 105, 20557-20564 (2000). 2. T. G. Slanger, P. C. Cosby, and D. L. Huestis, ``New Optical Emissions in the Terrestrial Nightglow: The O2({c - b}) Bands,'' submitted to AGU Spring 2002 Meeting. 3. K. S. Kalogerakis, A. Totth, P. C. Cosby, T. G. Slanger, and R. A. Copeland, Eos Trans. AGU 81(48), Fall Meet. Suppl., SA11A-39 (2000).
Amaral G. A.
Copeland Richard A.
Kalogerakis Konstantinos S.
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