Other
Scientific paper
May 2001
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2001agusm..sa31a21m&link_type=abstract
American Geophysical Union, Spring Meeting 2001, abstract #SA31A-21
Other
0310 Airglow And Aurora, 0394 Instruments And Techniques, 0399 General Or Miscellaneous
Scientific paper
Vibrationally excited hydroxyl radicals (υ = 6-9) are generated in the 80 to 100 km altitude range of the Earth's atmosphere by the reaction of atomic hydrogen with ozone. Low vibrational levels (υ < 5) are populated from the higher vibrational levels via collisions with molecular oxygen. For these low vibrational levels molecular oxygen relaxation is inefficient (1.3 - 17 x10-13 cm3-s-1 at room temperature [1]) and collisions with oxygen atoms may play an important role in the collisional lifetime in the atmosphere. Given the importance of O-atom collisions, we have developed an experimental approach and performed experiments on the collisional removal of OH(υ = 2) with O-atoms. In our experimental approach, we use the output of a pulsed excimer laser at 248 nm to photodissociate ozone in an O3/H2O/N2 mixture and the wavelength tunable output of a frequency-double Nd:YAG-pumped dye laser to probe the transient population of OH in the υ = 0, 1, and 2 vibrational levels using laser-induced fluorescence spectroscopy. Vibrationally excited OH molecules are produced, in vibrational levels up to and including υ = 2, through the exothermic reaction of O(1D) with water. By adjusting the composition of the O3/H2O/N2 mixture and by varying the 248 nm laser fluence to control the ozone dissociation fraction, the dominant relaxation partner can be varied systematically from ozone and water to atomic oxygen. We can dissociate > 90% of the ozone in the beam with easily obtainable laser fluences, generating copious amounts of O atoms. Using this method we obtained a preliminary rate constant of 4 \pm 1 x10-11 cm3-s-1 for removal of OH(υ = 2) with O atoms. This rate constant is only slightly larger than the value of 3.3 \pm 0.7 x10-11 cm3-s-1 for the reaction of OH(υ = 0) with O atoms to generate H atoms and oxygen molecules [2]. This weak dependence of OH loss rates on vibrational excitation is in contrast to previous measurements indicating a factor of 3 to 5 increase going from υ = 0 to υ = 1 [3]. In the presentation we will compare our results with the only other laboratory results and theoretical calculations. Preliminary results on the mechanism of the relaxation will also be presented. This work is supported by the Aeronomy Program of the National Science Foundation (ATM -9909807). [1] Dodd, J. A, Lipson, S. J., and Blumberg, W. A. M., J. Chem. Phys., 95, 5752-5762, 1991. [2] DeMore, W. B., and 8 co-authors, NASA Publication JPL-97-4, January 15, 1997. [3] Spencer J. E, and Glass, G. P., Int. J. Chem. Kinetics, 9, 97-109 and 111-122, 1977.
Copeland Richard A.
Kalogerakis Konstantinos S.
Marschall Jochen
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