Download Dodd et al.

Laboratory Measurement of CO2(2) + O
Temperature-Dependent Vibrational Energy Transfer
Karen J.
1
Castle,
1
Simione,
Michael
Eunsook S.
2
Hwang,
and James A. Dodd
Air Force Research Laboratory, Space Vehicles Directorate, Hanscom Air Force Base, MA 01731 USA
1Department of Chemistry, Bucknell University, Lewisburg, PA 17837 USA
2Stewart Radiance Laboratory, Bedford, MA 01730 USA
Temperature Dependence of kO(2)
Experimental Setup
Motivation
• CO2(2) - O vibrational energy transfer (VET) key process in the
upper atmosphere
Literature Predictions
• Analysis of ATMOS data suggests negligible or weakly
negative temperature dependence for kO(2)
• Implicated in thermospheric global cooling
• Long-term effects on thermospheric temperature, density structure:
satellite drag and longevity
• M. Lopez-Puertas et al., J. Geophys. Res. 97, 20469 (1992)
• Recent quantum mechanical treatment predicts kO(2) 
exp(T-1/3) for O(3PJ=0,1), and a dominant temperatureindependent kO(2) for O(3PJ=2)
• Process:
• CO2(0000) + O  CO2(0110) + O
• CO2(0110)  CO2(0000) + 15 mm
• Overall, kO(2)  T1/2 dependence is predicted
• Discrepancy between laboratory and field data-derived
measurements of kO(2)
• Laboratory: (1.2-1.8)  10-12 cm3s-1 (see below)
• Field data: (36)  10-12 cm3s-1
CO2 Spectroscopy
a)
Figure from M.P. de laraCastells, M.I. Hernandez,
G. Delgado-Barrio, P.
Villareal, and M. LopezPuertas, Mol. Phys. 105,
1171 (2007)
b)
3000
1
01 1
*
2.5e-19
1
2.0e-19
0
-1
Reference
300
Shved et al., 1991
1500
0
10 0
0
02 0
*
*
2
02 0
*
1000
1
01 0
*
500
1.2  0.2
Pollock et al., 1993;
Scott et al., 1993
295
0
0
0
*
0
(00 0)
R(36)
1.0e-19
2
(02 0)
P(20)
1.8  0.3
300-358
Khvorostovskaya et al., 2002
318
Castle et al., 2006
(1000)
P(22)
2
(02 0)
P(19)
**
0
(00 0)
P(29)
5.0e-20
Laboratory Result
1
2
2307.0
3
2307.2
2307.4
2307.6
2307.8
2308.0
2308.2
2308.4
2308.6
-1
CO2(mn p) l Value
a) Nine lowest-energy CO2 vibrational levels, plus the (0111) level, plotted as a function
of vibrational angular momentum l. Two v3  (v3+1) diode laser absorption transitions
are indicated. Populations labeled with the asterisk (*) have been detected in this work
b) Diode laser absorption spectrum of CO2 in the 2308 cm-1 region. The lower
vibrational states are labeled and all transitions are v3  (v3+1). The single * denotes
the 16O13C16O isotope while the double ** indicates the 18O12C16O isotope
Experimental Approach
Population Time Evolution
8
• Variable temperature measurements
• Cold temperature – use vacuum-jacketed cell with solvent or liquid
nitrogen coolant
• High temperature – wrap cell with heating tape
1.5
1.0
0.5
150
200
250
300
350
400
450
500
4
2
• Pulsed, fourth-harmonic Nd:YAG laser excitation
0
CO2 (0110)-(0111) P(36)
TDLAS signal for five
different O-atom
densities at a cell
temperature of 250 K.
The green lines represent
the predicted population
time evolution from a
global nonlinear least
squares fit
8
6
4
2
Relative Intensity
• Use intense v3  (v3+1) transitions
2.0
kO(2) as a function of
reaction cell
temperature. The rate
coefficient exhibits a
modest negative
temperature
dependence. Error
bars of  15% have
been assigned to
account for
uncertainty in various
experimental
parameters.
Temperature (K)
6
• 0.15-0.30% CO2, 0.05-1.0% O3, balance Xe
• CW diode laser detection of time-dependent CO2 vibrational level
populations
2.5
0.0
100
• Slow-flowing gas mixture with pTOT = 6-12 Torr
• O3 + 266 nm  O(1D) + O2(1g)
• Xe quenches O(1D), minimizes energy transfer to CO2
• Stimulates 5-50 K temperature jump
3.0
Wavenumber (cm )
l
1.4  0.2
**
0
(00 0)
P(30)
0.0
00 0
*
1.5e-19
3 -1
1.5  0.5
Temp (K)
*
3
03 0
cm s )
cm3s-1)
11 0
1
03 0
-12
kO(2)
(10-12
1
2000
Intensity (arb. units)
00 1
*
Rate Constant (10
2500
Term Energy (cm )
Laboratory Measurements of kO(2) Near 300 K
(01 0)
P(33)
0
8
6
4
2
0
8
6
4
2
0
Summary
• A new apparatus has been constructed using diode laser
detection to study VET in CO2-O collisions in the 150-500 K
range
• The measured rate coefficients show a negative temperature
dependence with kO(2) values ranging from 2.310-12 cm3s-1
(165 K) to 1.310-12 cm3s-1 (475 K)
Acknowledgment
8
6
4
2
0
0
1000
2000
3000
Delay Time (ms)
4000
5000
NASA Geospace Sciences
The Camille & Henry Dreyfus Foundation
Bucknell University