HR: 0800h
AN: SA41A-1032 [Abstracts]
TI: Rate Coefficient for Collisional Removal of O$_2$($X^3\Sigma^-_g$, $v$ = 1) with O Atoms at 240
K
AU: * Pejakovi\'c, D A
EM: dusan.pejakovic@sri.com
AF: Molecular Physics Laboratory, SRI International, 333 Ravenswood Ave., Menlo Park, CA 94025
United States
AU: Campbell, Z
EM: zacharykeith@hotmail.com
AF: Molecular Physics Laboratory, SRI International, 333 Ravenswood Ave., Menlo Park, CA 94025
United States
AU: Kalogerakis, K S
EM: ksk@sri.com
AF: Molecular Physics Laboratory, SRI International, 333 Ravenswood Ave., Menlo Park, CA 94025
United States
AU: Copeland, R A
EM: richard.copeland@sri.com
AF: Molecular Physics Laboratory, SRI International, 333 Ravenswood Ave., Menlo Park, CA 94025
United States
AU: Slanger, T G
EM: tom.slanger@sri.com
AF: Molecular Physics Laboratory, SRI International, 333 Ravenswood Ave., Menlo Park, CA 94025
United States
AB:
Knowledge of the water concentration profile is key to understanding of the chemistry and energy flow in the stratosphere and
mesosphere. One of the tasks of the SABER instrument in NASA$'$s TIMED mission is to measure water vapor concentration by
detecting H$_2$O($\nu_2$) emission in the 6.8 $\mu$m region. An important source of the H$_2$O($\nu_2$) emission is the
collisional deactivation of vibrationally excited O$_2$: O$_2$($X^3\Sigma^-_g$, $v$ = 1) + H$_2$O $\leftrightarrow$
O$_2$($X^3\Sigma^-_g$, $v$ = 0) + H$_2$O($\nu_2$). For reliable interpretation of the SABER data it is crucial to determine
rate coefficient for the competing process: O$_2$($X^3\Sigma^-_g$, $v$ = 1) + O($^3P$) $\rightarrow$ O$_2$($X^3\Sigma^-_g$,
$v$ = 0) + O($^3P$) [1].
Laboratory measurements are reported of the rate coefficient for collisional removal of
O$_2$($X^3\Sigma^-_g$, $v$ = 1) by O($^3P$) at a temperature of 240 K, relevant to the upper mesosphere. Instead of directly
detecting the O$_2$($X^3\Sigma^-_g$, $v$ = 1) population, a novel, technically simpler, approach is used in which the $v$ =
1 level of the O$_2$($a^1\Delta_g$) state is monitored. With ground-state O$_2$ present, owing to the rapid equilibration of
the O$_2$($X^3\Sigma^-_g$, $v$ = 1) and O$_2$($a^1\Delta_g$, $v$ = 1) populations via the processes O$_2$($a^1\Delta_g$, $v$
= 1) + O$_2$($X^3\Sigma^-_g$, $v$ = 0) $\leftrightarrow$ O$_2$($a^1\Delta_g$, $v$ = 0) + O$_2$($X^3\Sigma^-_g$, $v$ = 1),
the information on the O$_2$($X^3\Sigma^-_g$, $v$ = 1) kinetics is extracted from the O$_2$($a^1\Delta_g$, $v$ = 1) temporal
evolution. A two-laser method is employed, in which the pulsed output of the first laser near 285 nm photodissociates ozone
to produce atomic oxygen and O$_2$($a^1\Delta_g$, $v$ = 1), and the pulsed output of the second laser detects
O$_2$($a^1\Delta_g$, $v$ = 1) via the resonance-enhanced multiphoton ionization. In the same experiment, rate coefficients
for removal of O$_2$($a^1\Delta_g$, $v$ = 1) with the atmospherically relevant colliders O$_2$, CO$_2$, and O also were
measured at room temperature and 240 K.
The measured rate coefficient for O$_2$($X^3\Sigma^-_g$, $v$ = 1) removal by O($^3P$) is in the range 2--3 $\times$
10$^{-12}$ cm$^3$s$^{-1}$ at 240 K, compared to the recently measured room temperature value of about 3 $\times$ 10$^{-12}$
cm$^3$s$^{-1}$ [2]. Interestingly, removal of O$_2$($a^1\Delta_g$, $v$ = 1) by O($^3P$) is about five times less efficient
than removal of O$_2$($X^3\Sigma^-_g$, $v$ = 1). The rate coefficient for O$_2$($a^1\Delta_g$, $v$ = 1) removal by O$_2$ is
in the range 5--6 $\times$ 10$^{-11}$ cm$^3$s$^{-1}$ and is nearly temperature independent in the region 296--240 K. The
removal by CO$_2$ is about 3000 times slower than removal by O$_2$ and nearly independent on temperature. Implications of
the results for atmospheric modeling will be discussed.
This work is supported by the NASA Geospace Sciences Program under grant NAG5-13002. Participation of Z. Campbell was made
possible through the NSF Research Experience for Undergraduates Program under grant PHY-0353745.
[1] M. G. Mlynczak, D. K. Zhou, M. Lopez-Puertas, G. Zaragoza, and J. M. Russell, Geophys. Res. Lett. 26, 63 (1999).
[2] Konstantinos S. Kalogerakis, Richard A. Copeland, and Tom G. Slanger, Eos. Trans. AGU 82(47), Fall Meet. Suppl., Abstract
SA41B-0728, 2001.
DE: 5405 Atmospheres--composition and chemistry
DE: 5435 Ionospheres (2459)
DE: 0310 Airglow and aurora
DE: 0343 Planetary atmospheres (5405, 5407, 5409, 5704, 5705, 5707)
SC: SPA-Aeronomy [SA]
MN: 2004 AGU Fall Meeting