Laboratory Measurements of the O2(a1Δ g, v = 0) and O2(b1Σ ^+g, v = 0) Yields Following Collisional Removal of O2(A3Σ ^+u, v = 6--10)

Details Laboratory Measurements of the O2(a1Δ g, v = 0) and O2(b1Σ ^+g, v = 0) Yields Following Collisional Removal of O2(A3Σ ^+u, v = 6--10) Laboratory Measurements of the O2(a1Δ g, v = 0) and O2(b1Σ ^+g, v = 0) Yields Following Collisional Removal of O2(A3Σ ^+u, v = 6--10)

Dec 2003

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2003agufmsa12a1075p&link_type=abstract

American Geophysical Union, Fall Meeting 2003, abstract #SA12A-1075

Physics

0310 Airglow And Aurora, 0343 Planetary Atmospheres (5405, 5407, 5409, 5704, 5705, 5707)

Scientific paper

Three-body oxygen atom recombination presents a major source of the nightglows of Earth and Venus. In this process the O2 molecule is formed in the seven electronic states that lie below the O(3P) + O(3P) dissociation limit. Information on the yields of the lowest O2 electronically excited states, a1Δg and b1Σ ^+g, from O-atom recombination can be used to extract O-atom densities in the emitting atmospheric region from the atmospheric emission intensities in the O2(a1Δ g--X3Σ ^-g) and O2(b1Σ ^+g--X3Σ ^-g) bands. Previous SRI experiments showed rapid collisional transfer between the excited states in the energy region close to the dissociation limit [1]. Based on this, we argue that direct optical excitation to these states (c1Σ ^-u, A'3Δ u, A3Σ ^+u) and the resulting energy flow is a reasonable proxy for the three-body O-atom recombination. This work presents studies of vibration level- and collider-dependent yields into the v = 0 levels of the a1Δ g and b1Σ ^+g states, following collisional deactivation of the v = 6-10 levels of the A3Σ ^+u state. Experiments are done at 240 K, a temperature slightly higher than temperatures relevant for the Earth's mesopause (altitude 80-100 km). Colliders pertinent to the atmospheres of Earth and Venus, O2, N2, and CO2, are used. We employ a state-selective two-laser method, in which pulsed output of the first laser excites O2 to O2(A, v = 6--10). A time-delayed second laser pulse detects O2(a, v = 0) and O2(b, v = 0) by resonance-enhanced multiphoton ionization via the d1Π g Rydberg state. Temporal evolution of the O2(a, v = 0) and O2(b, v = 0) populations is determined by varying the time delay between the two laser pulses. We find that the O2(a, v = 0) yields from O2(A, v = 7--9) are nearly equal, while the yields from O2(A, v = 6 and 10) are lower by 30-40%. The O2(b, v = 0) yields are nearly equal for O2(A, v = 8--10), and lower by 40-50% for O2(A, v = 6 and 7). Temporal evolution of the O2(a, v = 0) signal following excitation to O2(A, v = 8) shows that production of O2(a, v = 0) occurs through a rapid several-step collision-driven process. Experiments with air show O2(a, v = 0) yield about 60% lower than the yield from pure O2. Production of O2(a, v = 0) in air is about 3.5 times slower than in pure O2. The O2(b, v = 0) yield from air is about the same as the yield from pure O2. The results indicate that N2 collider is not more efficient than O2 in promptly producing O2(a, v = 0) and O2(b, v = 0). Preliminary experiments with CO2 show that CO2 collider is likely less efficient than O2 in producing O2(a, v = 0). We will outline our current efforts to use comparison with products from a O3/O2 mixture to determine the absolute O2(a, v = 0) and O2(b, v = 0) yields as well as relative yields of these two states. Preliminary results show that about 2.5 times as much O2(a, v = 0) as O2(b, v = 0) is promptly formed upon O2(A) excitation. This work is funded by the NASA Ionosphere, Thermosphere, and Mesosphere Supporting Research & Technology Program and the NASA Planetary Atmospheres Program. [1] T.G. Slanger and R. A. Copeland, ``Energetic Oxygen in the Upper Atmosphere and the Laboratory'', Chem. Rev., in press.

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