Physics
Scientific paper
Dec 2005
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2005agufmsa11a0216s&link_type=abstract
American Geophysical Union, Fall Meeting 2005, abstract #SA11A-0216
Physics
0340 Middle Atmosphere: Composition And Chemistry
Scientific paper
The temperature dependence of the OH + O -> H + O2 reaction was measured using a laser photolysis - laser induced fluorescence technique. A known excess of O atoms is prepared by complete 248 nm laser photolysis of a monitored O3 flow in N2, with small amounts of H2 to provide an OH source. The window-equipped flow cell is enclosed in a Dewar by which temperatures of 140K (LN2), 235K (dry ice), and 365K (heated cell) were produced. Modeled results for OH(v=0) + O under various conditions agree with the NASA-JPL panel recommendation at 298 K, independent of OH source, with a slightly larger temperature dependence. k(140K) = 2.5 k(298K). Measured decays for OH(v=4) reflect reaction, and vibrational relaxation by O and by the O2(1-delta) also created by the O3 photolysis. Results show a considerable increase in decay rate for v=4 at all temperatures, likely from vibrational relaxation processes. k(228K) = 1.9 x 10(-10). Interpreting the results from the perspective of an HO2 intermediate and past theoretical efforts reveals some challenges. We also measured a removal rate constant of 1.2 x 10(-12) (298K) by added O2.
Experiments were performed at 140 K for trace amounts of OH and O (<1 mtorr) in 40 torr O2 or N2 to search for evidence of the proposed weakly bound HO3 atmospheric complex. Signal intensities and slow decays are identical, which provides an upper limit of 7 kcal/mole for the stability of this species. Research supported by the NSF Aeronomy Program and NASA Geoscience ITM Physics Program.
Robertson Richard
Smith Graham P.
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