Laboratory Measurement of CO2(2) + OTemperature-Dependent Vibrational Energy Transfer

Karen J. Castle,1 Michael Simione,1 Eunsook S. Hwang,2 and James A. DoddAir 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

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

• 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 2.310-12 cm3s-1 (165 K) to 1.310-12 cm3s-1 (475 K)

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

kO(2) (10‑12 cm3s‑1) Temp (K) Reference

1.5 0.5 300 Shved et al., 1991

1.2 0.2 295Pollock et al., 1993;

Scott et al., 1993

1.4 0.2 300-358 Khvorostovskaya et al., 2002

1.8 0.3 318 Castle et al., 2006

CO2 Spectroscopy

Population Time Evolution

Laboratory Measurements of kO(2) Near 300 K

• Slow-flowing gas mixture with pTOT = 6-12 Torr

• 0.15-0.30% CO2, 0.05-1.0% O3, balance Xe

• Pulsed, fourth-harmonic Nd:YAG laser excitation• O3 + 266 nm O(1D) + O2(1g)

• Xe quenches O(1D), minimizes energy transfer to CO2

• Stimulates 5-50 K temperature jump

• CW diode laser detection of time-dependent CO2 vibrational level populations

• Use intense v3 (v3+1) transitions

• Variable temperature measurements• Cold temperature – use vacuum-jacketed cell with solvent or liquid

nitrogen coolant

• High temperature – wrap cell with heating tape

Motivation• CO2(2) - O vibrational energy transfer (VET) key process in the

upper atmosphere• Implicated in thermospheric global cooling

• Long-term effects on thermospheric temperature, density structure: satellite drag and longevity

• Process:

• CO2(0000) + O CO2(0110) + O

• CO2(0110) CO2(0000) + 15 m

• Discrepancy between laboratory and field data-derived measurements of kO(2)

• Laboratory: (1.2-1.8) 10-12 cm3s-1 (see below)

• Field data: (36) 10-12 cm3s-1Figure from M.P. de lara-Castells, M.I. Hernandez, G. Delgado-Barrio, P. Villareal, and M. Lopez-Puertas, Mol. Phys. 105, 1171 (2007)

0111

0220

0000

0110

033011100310

0200

0001

1000

*

*

* **

*

*

*

CO2(mnlp) l Value

0 1 2 3

Term

En

erg

y (

cm-1

)

0

500

1000

1500

2000

2500

3000

Temperature Dependence of kO(2)

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.

Experimental Setup

Literature Predictions• Analysis of ATMOS data suggests negligible or weakly

negative temperature dependence for kO(2)

• 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 temperature-independent kO(2) for O(3PJ=2)

• Overall, kO(2) T1/2 dependence is predicted

Wavenumber (cm-1)

2307.0 2307.2 2307.4 2307.6 2307.8 2308.0 2308.2 2308.4 2308.6

In

ten

sit

y (

arb

. u

nit

s)

0.0

5.0e-20

1.0e-19

1.5e-19

2.0e-19

2.5e-19

(1000)P(22)

(0110)P(33)

* *(0000)P(30)

(0220)P(20)

*(0000)R(36)

(0220)P(19)

* *(0000)P(29)

a) b)

Experimental Approach

Summary

NASA Geospace SciencesThe Camille & Henry Dreyfus Foundation

Bucknell University

Acknowledgment

Laboratory Result

0

2

4

6

8

Rela

tive I

nte

nsit

y

0

2

4

6

8

0

2

4

6

8

Delay Time (ms)

0 1000 2000 3000 4000 5000

0

2

4

6

8

0

2

4

6

8

Temperature (K)

100 150 200 250 300 350 400 450 500

Rate

Con

sta

nt

(10

-12 c

m3s

-1)

0.0

0.5

1.0

1.5

2.0

2.5

3.0