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

HCFC-142b in the atmosphere HCFC-142b (CF 2 Cl-CH 3 ) is a substitute to CFC-11 ODP = 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.

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.

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 ( 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

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 )

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 )

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.

Data validation Temperature (K)Absorption bandThis workPNNL (277K) Newnham and Ballard, 1995 Clerbaux et al., 1993 Cappellani and Restelli, , , 5, , 3, , , 5, , 3, , , 5, , 3,

Data validation Temperature (K)Absorption bandThis workPNNL (277K) Newnham and Ballard, 1995 Clerbaux et al., 1993 Cappellani and Restelli, , , 5, , 3, , , 5, , 3, , , 5, , 3,

Integrated strengths vs temperature

Data validation Temperature (K)Absorption bandThis workPNNL (277K) Newnham and Ballard, 1995 Clerbaux et al., 1993 Cappellani and Restelli, , , 5, , 3, , , 5, , 3, , , 5, , 3,

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

Comparison with DFT

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.