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Laboratory Measurement of CO 2 ( 2 ) + O Temperature-Dependent Vibrational Energy Transfer Karen J. Castle, 1 Michael Simione, 1 Eunsook S. Hwang, 2 and.

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Presentation on theme: "Laboratory Measurement of CO 2 ( 2 ) + O Temperature-Dependent Vibrational Energy Transfer Karen J. Castle, 1 Michael Simione, 1 Eunsook S. Hwang, 2 and."— Presentation transcript:

1 Laboratory Measurement of CO 2 ( 2 ) + O Temperature-Dependent Vibrational Energy Transfer Karen J. Castle, 1 Michael Simione, 1 Eunsook S. Hwang, 2 and James A. Dodd Air Force Research Laboratory, Space Vehicles Directorate, Hanscom Air Force Base, MA USA 1 Department of Chemistry, Bucknell University, Lewisburg, PA USA 2 Stewart Radiance Laboratory, Bedford, MA USA CO 2 (01 1 0)-(01 1 1) 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 CO 2 -O collisions in the K range The measured rate coefficients show a negative temperature dependence with k O ( 2 ) values ranging from 2.3  cm 3 s -1 (165 K) to 1.3  cm 3 s -1 (475 K) a) Nine lowest-energy CO 2 vibrational levels, plus the (01 1 1) level, plotted as a function of vibrational angular momentum l. Two v 3  (v 3 +1) diode laser absorption transitions are indicated. Populations labeled with the asterisk (*) have been detected in this work b) Diode laser absorption spectrum of CO 2 in the 2308 cm -1 region. The lower vibrational states are labeled and all transitions are v 3  (v 3 +1). The single * denotes the 16 O 13 C 16 O isotope while the double ** indicates the 18 O 12 C 16 O isotope k O ( 2 ) (10 ‑ 12 cm 3 s ‑ 1 ) Temp (K)Reference 1.5  Shved et al.,  Pollock et al., 1993; Scott et al.,  Khvorostovskaya et al.,  Castle et al., 2006 CO 2 Spectroscopy Population Time Evolution Laboratory Measurements of k O ( 2 ) Near 300 K Slow-flowing gas mixture with p TOT = 6-12 Torr % CO 2, % O 3, balance Xe Pulsed, fourth-harmonic Nd:YAG laser excitation O nm  O( 1 D) + O 2 ( 1  g ) Xe quenches O( 1 D), minimizes energy transfer to CO 2 Stimulates 5-50 K temperature jump CW diode laser detection of time-dependent CO 2 vibrational level populations Use intense v 3  (v 3 +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 CO 2 ( 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: CO 2 (00 0 0) + O  CO 2 (01 1 0) + O CO 2 (01 1 0)  CO 2 (00 0 0) + 15  m Discrepancy between laboratory and field data-derived measurements of k O ( 2 ) Laboratory:( )  cm 3 s -1 (see below) Field data:(3  6)  cm 3 s -1 Figure from M.P. de lara- Castells, M.I. Hernandez, G. Delgado-Barrio, P. Villareal, and M. Lopez- Puertas, Mol. Phys. 105, 1171 (2007) Temperature Dependence of k O ( 2 ) k O ( 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 k O ( 2 ) M. Lopez-Puertas et al., J. Geophys. Res. 97, (1992) Recent quantum mechanical treatment predicts k O ( 2 )  exp(T -1/3 ) for O( 3 P J=0,1 ), and a dominant temperature- independent k O ( 2 ) for O( 3 P J=2 ) Overall, k O ( 2 )  T 1/2 dependence is predicted a) b) Experimental Approach Summary NASA Geospace Sciences The Camille & Henry Dreyfus Foundation Bucknell University Acknowledgment Laboratory Result


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