HR: 1330h
AN: SA12A-1076    [PDF]
TI: Temperature Dependent Collisional Energy Transfer of N$_2$ ($a^1\Pi_g$ and $a'^1\Sigma_u$, $v=0$ and 1)
AU: Khachatrian, A
EM: ani.k@jhu.edu
AF: Institute of Physical Sciences and Technology, University of Maryland, College Park, MD 20742 United States
AU: Khachatrian, A
EM: ani.k@jhu.edu
AF: Visiting Scientist at SRI International, 333 Ravenswood Avenue, Menlo Park, CA 94025 United States
AU: Khachatrian, A
EM: ani.k@jhu.edu
AF: Present address: Department of Chemistry, The Johns Hopkins University, Remsen Hall, 3400 N Charles Street, Baltimore, MD 21218 United States
AU: * Wouters, E R
EM: ewouters@umd.edu
AF: Institute of Physical Sciences and Technology, University of Maryland, College Park, MD 20742 United States
AU: * Wouters, E R
EM: ewouters@umd.edu
AF: Visiting Scientist at SRI International, 333 Ravenswood Avenue, Menlo Park, CA 94025 United States
AU: Gudipati, M S
EM: mgudipati@mail.arc.nasa.gov
AF: Institute of Physical Sciences and Technology, University of Maryland, College Park, MD 20742 United States
AU: Gudipati, M S
EM: mgudipati@mail.arc.nasa.gov
AF: Visiting Scientist at NASA Ames Research Center, Mail Stop 245-6, Moffett Field, CA 94035 United States
AU: Ginter, M L
AF: Institute of Physical Sciences and Technology, University of Maryland, College Park, MD 20742 United States
AU: Copeland, R A
EM: richard.copeland@sri.com
AF: Aeronomy Group, Molecular Physics Laboratory, SRI International, 333 Ravenswood Avenue, Menlo Park, CA 94025 United States
AB: Lyman-Birge-Hopfield (LBH) emission of molecular nitrogen ($a^1\Pi_g$ -- $X^1\Sigma_g^+$) 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 $a^1\Pi_g$, $a'^1\Sigma_u$, and $w^1\Delta_u$. 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 N$_2$($a^1\Pi_g$, $v$=0, 1) and N$_2$($a'^1\Sigma_u$, $v$=0, 1) with N$_2$, O$_2$, and O colliders at 150, 240, and 300 K. In our experiments, ground state N$_2$ molecules are excited to the $v$=1 level of the $a^1\Pi_g$ state via a two-photon transition by the first laser pulse. A second laser probes either N$_2$($a^1\Pi_g$, $v$=1) or the products of collisionally induced energy transfer, N$_2$($a^1\Pi_g$, $v$=0) or N$_2$($a'^1\Sigma_u$, $v$=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 N$_2$ the rate constants for N$_2$($a^1\Pi_g$, $v$=0) and N$_2$($a^1\Pi_g$, $v$=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 O$_2$ and O colliders the rate constants for N$_2$($a^1\Pi_g$, $v$=1) removal are faster than that for N$_2$ by about 15 times and more than 50 times, respectively. For the first time, the temporal evolution of N$_2$($a'^1\Sigma_u$, $v$=0) and N$_2$($a'^1\Sigma_u$, $v$=1) is observed directly. The results for collisional removal of N$_2$($a'^1\Sigma_u$, $v$=0) are in agreement with previous indirect measurements in the literature. For N$_2$($a'^1\Sigma_u$, $v$=1) at 300 K, the direct temporal evolution measurements show a total removal rate constant similar in magnitude to those for N$_2$($a^1\Pi_g$, $v$=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, {\it Geophys.\ Res.\ Lett.\ }{\bf 18} (1991) 689. [2] R.W. Eastes, {\it J. Geophys.\ Res.\ }{\bf 105} (2000) 18557.
DE: 0300 ATMOSPHERIC COMPOSITION AND STRUCTURE
DE: 0310 Airglow and aurora
DE: 0317 Chemical kinetic and photochemical properties
DE: 0343 Planetary atmospheres (5405, 5407, 5409, 5704, 5705, 5707)
SC: SPA - Aeronomy [SA]
MN: 2003 Fall Meeting