Temperature Dependent Collisional Energy Transfer of N2 (a1Πg and a'1Σu, v=0 and 1)

Details Temperature Dependent Collisional Energy Transfer of N2 (a1Πg and a'1Σu, v=0 and 1) Temperature Dependent Collisional Energy Transfer of N2 (a1Πg and a'1Σu, v=0 and 1)

Dec 2003

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2003agufmsa12a1076k&link_type=abstract

American Geophysical Union, Fall Meeting 2003, abstract #SA12A-1076

Other

0300 Atmospheric Composition And Structure, 0310 Airglow And Aurora, 0317 Chemical Kinetic And Photochemical Properties, 0343 Planetary Atmospheres (5405, 5407, 5409, 5704, 5705, 5707)

Scientific paper

Lyman-Birge-Hopfield (LBH) emission of molecular nitrogen (a1Π g -- X1Σ g^+) has been a rich source of information on the atmospheres of nitrogen-abundant planets and moons. Accurate modeling of the altitude-dependent LBH emission in airglow and aurora of the Earth would be an important step for remote sensing of the atmospheres of other planets and satellites in our solar system, such as Titan and Triton [1]. Recent models [2] incorporate collisionally induced electronic transitions (CIET) among the three nested singlet electronic states a1Π g, a'1Σ u, and w1Δ u. However, several rate constants have to be estimated due to the lack of laboratory experimental data on the energy transfer processes and their temperature dependence. We have carried out two-color, pump-probe, resonance-enhanced multiphoton ionization (REMPI) experiments to determine collisional removal rate constants of N2(a1Π g, v=0, 1) and N2(a'1Σ u, v=0, 1) with N2, O2, and O colliders at 150, 240, and 300 K. In our experiments, ground state N2 molecules are excited to the v=1 level of the a1Π g state via a two-photon transition by the first laser pulse. A second laser probes either N2(a1Π g, v=1) or the products of collisionally induced energy transfer, N2(a1Π g, v=0) or N2(a'1Σ u, v=0 and 1). The temporal evolution of the vibrational population is obtained by varying the time delay between the two pulses. Experimental results show that in the case of removal by N2 the rate constants for N2(a1Π g, v=0) and N2(a1Π g, v=1) are similar and in good agreement with the literature values at 300 K. The rate constants for both states are comparable at 240 and 300 K and increase by 50 to 100% at 150 K, i.e. slightly faster rate coefficients should be used in atmospheric models. In the case of O2 and O colliders the rate constants for N2(a1Π g, v=1) removal are faster than that for N2 by about 15 times and more than 50 times, respectively. For the first time, the temporal evolution of N2(a'1Σ u, v=0) and N2(a'1Σ u, v=1) is observed directly. The results for collisional removal of N2(a'1Σ u, v=0) are in agreement with previous indirect measurements in the literature. For N2(a'1Σ u, v=1) at 300 K, the direct temporal evolution measurements show a total removal rate constant similar in magnitude to those for N2(a1Π g, v=0 and 1). We acknowledge the support of the National Science Foundation Aeronomy Program via grant ATM 9910914. [1] D.F. Strobel, R.R. Meier, M.E. Summers, and D.J. Strickland, Geophys. Res. Lett. 18 (1991) 689. [2] R.W. Eastes, J. Geophys. Res. 105 (2000) 18557.

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