Physics
Scientific paper
Dec 2004
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2004agufmsa41a1032p&link_type=abstract
American Geophysical Union, Fall Meeting 2004, abstract #SA41A-1032
Physics
5405 Atmospheres: Composition And Chemistry, 5435 Ionospheres (2459), 0310 Airglow And Aurora, 0343 Planetary Atmospheres (5405, 5407, 5409, 5704, 5705, 5707)
Scientific paper
Knowledge of the water concentration profile is key to understanding of the chemistry and energy flow in the stratosphere and mesosphere. One of the tasks of the SABER instrument in NASA's TIMED mission is to measure water vapor concentration by detecting H2O(ν 2) emission in the 6.8 μ m region. An important source of the H2O(ν 2) emission is the collisional deactivation of vibrationally excited O2: O2(X3Σ ^-g, v = 1) + H2O <-> O2(X3Σ ^-g, v = 0) + H2O(ν 2). For reliable interpretation of the SABER data it is crucial to determine rate coefficient for the competing process: O2(X3Σ ^-g, v = 1) + O(3P) -> O2(X3Σ ^-g, v = 0) + O(3P) [1]. Laboratory measurements are reported of the rate coefficient for collisional removal of O2(X3Σ ^-g, v = 1) by O(3P) at a temperature of 240 K, relevant to the upper mesosphere. Instead of directly detecting the O2(X3Σ ^-g, v = 1) population, a novel, technically simpler, approach is used in which the v = 1 level of the O2(a1Δ g) state is monitored. With ground-state O2 present, owing to the rapid equilibration of the O2(X3Σ ^-g, v = 1) and O2(a1Δ g, v = 1) populations via the processes O2(a1Δ g, v = 1) + O2(X3Σ ^-g, v = 0) <-> O2(a1Δ g, v = 0) + O2(X3Σ ^-g, v = 1), the information on the O2(X3Σ ^-g, v = 1) kinetics is extracted from the O2(a1Δ g, v = 1) temporal evolution. A two-laser method is employed, in which the pulsed output of the first laser near 285 nm photodissociates ozone to produce atomic oxygen and O2(a1Δ g, v = 1), and the pulsed output of the second laser detects O2(a1Δ g, v = 1) via the resonance-enhanced multiphoton ionization. In the same experiment, rate coefficients for removal of O2(a1Δ g, v = 1) with the atmospherically relevant colliders O2, CO2, and O also were measured at room temperature and 240 K. The measured rate coefficient for O2(X3Σ ^-g, v = 1) removal by O(3P) is in the range 2--3 × 10-12 cm3s-1 at 240 K, compared to the recently measured room temperature value of about 3 × 10-12 cm3s-1 [2]. Interestingly, removal of O2(a1Δ g, v = 1) by O(3P) is about five times less efficient than removal of O2(X3Σ ^-g, v = 1). The rate coefficient for O2(a1Δ g, v = 1) removal by O2 is in the range 5--6 × 10-11 cm3s-1 and is nearly temperature independent in the region 296--240 K. The removal by CO2 is about 3000 times slower than removal by O2 and nearly independent on temperature. Implications of the results for atmospheric modeling will be discussed. This work is supported by the NASA Geospace Sciences Program under grant NAG5-13002. Participation of Z. Campbell was made possible through the NSF Research Experience for Undergraduates Program under grant PHY-0353745. [1] M. G. Mlynczak, D. K. Zhou, M. Lopez-Puertas, G. Zaragoza, and J. M. Russell, Geophys. Res. Lett. 26, 63 (1999). [2] Konstantinos S. Kalogerakis, Richard A. Copeland, and Tom G. Slanger, Eos. Trans. AGU 82(47), Fall Meet. Suppl., Abstract SA41B-0728, 2001.
Campbell Z.
Copeland Richard A.
Kalogerakis Konstantinos S.
Pejaković Dušan A.
Slanger Tom G.
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