New High-Resolution Absorption Cross-Section Measurements of

HCFC-142b in the Mid-IR Karine Le BrisSt Francis Xavier University, Nova Scotia, Canada

Kimberly StrongUniversity of Toronto, Ontario, Canada

Stella Melo Canadian Space Agency, Québec, Canada

HCFC-142b in the atmosphereHCFC-142b (CF2Cl-CH3) is a substitute to CFC-11

ODP = 0.065

GWP = 1800 for an horizon of 100 yearsComplete 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 (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

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.

CH3 str.

CH3 def.

CF2 str., C-C str.

C-Cl str., CF2 def.

C-C-Cl def.

CF2 str.

Data validationTemperature (K) Absorption band This work PNNL

(277K)Newnham and Ballard, 1995

Clerbaux et al., 1993

Cappellani and Restelli, 1992

273 8 0.70 0.736 0.70 0.69 0.75

7, 15 2.42 2.5 2.56 2.51 2.45

6,5,14 6.91 7.05 7.06 7.11 7.12

4,3,13 0.64 0.63 0.61 0.64 0.62

253 8 0.68 0.69 0.68

7, 15 2.36 2.41 2.40

6,5,14 6.76 6.16 6.96

4,3,13 0.65 0.65 0.78

233 8 0.67 0.71 0.754

7, 15 2.35 2.302 2.507

6,5,14 6.92 6.187 7.377

4,3,13 0.61 0.625 0.643

Data validationTemperature (K) Absorption band This work PNNL

(277K)Newnham and Ballard, 1995

Clerbaux et al., 1993

Cappellani and Restelli, 1992

273 8 0.70 0.736 0.70 0.69 0.75

7, 15 2.42 2.5 2.56 2.51 2.45

6,5,14 6.91 7.05 7.06 7.11 7.12

4,3,13 0.64 0.63 0.61 0.64 0.62

253 8 0.68 0.69 0.68

7, 15 2.36 2.41 2.40

6,5,14 6.76 6.16 6.96

4,3,13 0.65 0.65 0.78

233 8 0.67 0.71 0.754

7, 15 2.35 2.302 2.507

6,5,14 6.92 6.187 7.377

4,3,13 0.61 0.625 0.643

Integrated strengths vs temperature

Data validationTemperature (K) Absorption band This work PNNL

(277K)Newnham and Ballard, 1995

Clerbaux et al., 1993

Cappellani and Restelli, 1992

273 8 0.70 0.736 0.70 0.69 0.75

7, 15 2.42 2.5 2.56 2.51 2.45

6,5,14 6.91 7.05 7.06 7.11 7.12

4,3,13 0.64 0.63 0.61 0.64 0.62

253 8 0.68 0.69 0.68

7, 15 2.36 2.41 2.40

6,5,14 6.76 6.16 6.96

4,3,13 0.65 0.65 0.78

233 8 0.67 0.71 0.754

7, 15 2.35 2.302 2.507

6,5,14 6.92 6.187 7.377

4,3,13 0.61 0.625 0.643

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.