1. New High-Resolution Absorption Cross-Section Measurements of HCFC-142b in the Mid-IR Karine Le Bris St Francis Xavier University, Nova Scotia, Canada Kimberly Strong University of Toronto, Ontario, Canada Stella Melo Canadian Space Agency, Québec, Canada

2. HCFC-142b in the atmosphere HCFC-142b (CF 2 Cl-CH 3 ) is a substitute to CFC-11 ODP = 0.065 GWP = 1800 for an horizon of 100 years Complete phase-out scheduled for 2030 HCFC-142b annual global mean mole fractions from Oram et al., 1995, (blue), the AGAGE (green) and NOAA/ESRL (red) networks (O’Doherty et al., 2004; Montzka et al., 1999). From the Scientific Assessment of Ozone Depletion: 2006 Observed from space by the Canadian Atmospheric Chemistry Experiment (ACE) on the SCISAT-1 satellite mission.

3. Aim  Improve the available data by acquisition of new Fourier Transform IR spectroscopy spectra at higher resolution (0.02 cm -1 ) and a larger set of temperature (223K-283K).  Evaluate the evolution of the integrated cross sections with temperature.  Compare experimental results to theoretical values obtained by density functional theory.

4. Experimental conditions  FTS: Bomem DA8.002, 250 cm maximum optical path difference  Source: Globar, Beamsplitter: KBr, Detector: MCT  Pressure measurement: MKS baratrons  Temperature measurement: Omega ungrounded thermocouple inserted into the cell  Chiller: Nestlab ULT-80 with Syltherm XLT (200-533 K)  3.17-cm coolable cell with vacuum jacket  Elimination of the black body emission from the source aperture  Correction of the MCT detector non- linearity effect on the raw data

5. Experimental considerations  Spectral Range: 650 –3500 cm -1  Resolution: 0.02 cm -1  Temperature Range: 223K- 283K  Pressures: 2 to 12 torr  Data processing Removal of point from optically thin medium (z<0.1): increase the signal-to-noise ratio Removal of points from optically thick medium (z>1.1): elimination of saturation effect Extrapolation at 0-torr limit to eliminate collisional broadening on ro-vibrational transitions Wavenumber(cm -1 )

6. Experimental considerations  Spectral Range: 650 –3500 cm -1  Resolution: 0.02 cm -1  Temperature Range: 223K- 283K  Pressures: 2 to 12 torr  Data processing Removal of point from optically thin medium (z<0.1): increase the signal-to-noise ratio Removal of points from optically thick medium (z>1.1): elimination of saturation effect Extrapolation at 0-torr limit to eliminate collisional broadening on ro-vibrational transitions Wavenumber(cm -1 )

7. Survey spectrum Assignment done by comparison with theoretical results obtained by DFT (B3LYP and B3PW91) All the strong lines are inside the atmospheric windows and correspond to C-Cl or C-F vibrations modes. CH 3 str. CH 3 def. CF 2 str., C-C str. C-Cl str., CF 2 def. C-C-Cl def. CF 2 str.

8. Data validation Temperature (K)Absorption bandThis workPNNL (277K) Newnham and Ballard, 1995 Clerbaux et al., 1993 Cappellani and Restelli, 1992 273 8 0.700.7360.700.690.75 7, 15 2.422.52.562.512.45 6, 5, 14 6.917.057.067.117.12 4, 3, 13 0.640.630.610.640.62 253 8 0.680.690.68 7, 15 2.362.412.40 6, 5, 14 6.766.166.96 4, 3, 13 0.65 0.78 233 8 0.670.710.754 7, 15 2.352.3022.507 6, 5, 14 6.926.1877.377 4, 3, 13 0.610.6250.643

9. Data validation Temperature (K)Absorption bandThis workPNNL (277K) Newnham and Ballard, 1995 Clerbaux et al., 1993 Cappellani and Restelli, 1992 273 8 0.700.7360.700.690.75 7, 15 2.422.52.562.512.45 6, 5, 14 6.917.057.067.117.12 4, 3, 13 0.640.630.610.640.62 253 8 0.680.690.68 7, 15 2.362.412.40 6, 5, 14 6.766.166.96 4, 3, 13 0.65 0.78 233 8 0.670.710.754 7, 15 2.352.3022.507 6, 5, 14 6.926.1877.377 4, 3, 13 0.610.6250.643

10. Integrated strengths vs temperature

11. Data validation Temperature (K)Absorption bandThis workPNNL (277K) Newnham and Ballard, 1995 Clerbaux et al., 1993 Cappellani and Restelli, 1992 273 8 0.700.7360.700.690.75 7, 15 2.422.52.562.512.45 6, 5, 14 6.917.057.067.117.12 4, 3, 13 0.640.630.610.640.62 253 8 0.680.690.68 7, 15 2.362.412.40 6, 5, 14 6.766.166.96 4, 3, 13 0.65 0.78 233 8 0.670.710.754 7, 15 2.352.3022.507 6, 5, 14 6.926.1877.377 4, 3, 13 0.610.6250.643

12. Temperature dependency Strong T- dependence of the line shapes. The difference can be as large as 93% for a temperature decrease of 60 K.

13. Comparison with DFT

14. Conclusions  New high resolution (0.02cm -1 ) cross section measurements of HCFC-142b are now available in the range 223K-283K.  No variation of the integrated intensity strengths with temperature has been observed.  Good concordance between DFT calculation and experience.