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| Titel |
Laboratory Investigation of Relaxation Pathways for Vibrationally Excited OH |
| VerfasserIn |
K. S. Kalogerakis, J. Thiebaud, D. Matsiev, R. A. Copeland |
| Konferenz |
EGU General Assembly 2012
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 14 (2012) |
| Datensatznummer |
250060553
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| Zusammenfassung |
| The hydroxyl radical is a key species in the energy budget of the terrestrial atmospheres. In
the Earth’s upper atmosphere, vibrationally excited OH radicals (v -¤ 9) are formed by the H
+ O3 reaction. The non-thermal vibrational energy is either emitted as an infrared (IR) or
visible photon, or converted into translational and internal energy via collisions with ambient
gases. OH emission was recently reported for the first time in the nightglow of Venus [1].
Model calculations of the Mars airglow have also shown that the predicted intensity of
the OH emission is extremely sensitive to the pathway of vibrational relaxation
[2].
Accurate rate constant and mechanistic pathway information for the deactivation of the
OH(v) states is essential in the modeling of both the atmospheric OH emission and the
heating efficiency of the H + O3 reaction, as exemplified in our studies of vibrational
relaxation for OH(v = 7, 9) by O, O2, N2, and CO2 [3,4].
We have initiated a research program to investigate the key pathways involved in OH(v)
vibrational relaxation and their dependence on the collider species and temperature. In the
laboratory experiments, we probe the fraction of collisions that lead to single-quantum
relaxation of OH(v = 8) to OH(v = 7) for different atmospheric colliders. We developed a
three-laser approach using the following steps: (1) generation of OH(v -¤ 4) by the O(1D) +
H2 reaction following ozone photolysis at 248 nm by an KrF excimer laser in a mixture
containing nitrogen and hydrogen; (2) infrared overtone excitation of the OH(v = 4) radicals
to v = 7 at 938 nm using a pulsed optical parametric oscillator system triggered
when the v = 4 population is near maximum and; (3) detection of the OH(v = 7)
population by laser-induced fluorescence using the B - X (0,7) band at 213 nm with a
pulsed tunable dye laser timed in order to scan the delay with respect to the IR pump
laser.
We will present the experimental methodology and measurements on the relaxation of
OH(v = 8) to OH(v = 7) by O atoms and CO2. Our measurements to date indicate that
different collider gases favor distinct relaxation pathways: the single-quantum cascade
branching ratio for collisions with CO2 is approximately 3 times larger than that for collisions
with O atoms. We will also discuss the atmospheric implications of our results based on the
most current modeling calculations.
Research supported by NASA Geospace Science grants NNX08AM47G and
NNX12AD09G.
[1] Piccioni, G. et al., Astron. Astrophys. 483, L29-L33 (2008).
[2] García Muñoz, A. et al., Icarus 176, 75-95 (2005).
[3] Thiebaud, J., Kalogerakis, K.S., and Copeland, R.A., Fall AGU Meeting, Abstract
SA43A-1752 (2010).
[4] Kalogerakis, K.S., G.P. Smith, and R.A. Copeland, J. Geophys. Res. 116, D20307,
2011JD015734 (2011). |
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