1. Infrared absorption cross sections of cold propane in the low frequency region between 600 – 1300 cm-1.
Wong, A.a, Hargreaves, R.J.b, Billinghurst, B.E.c, Bernath, P.F.a
aDepartment of Chemistry and Biochemistry, Old Dominion University, Norfolk, VA, USA
bAtmospheric, Oceanic & Planetary Physics, Oxford University, Oxford, United Kingdom
cEFC, Canadian Light Source Inc., Saskatoon, Saskatchewan, Canada
FA03

2. Outline Introduction Experimental Results Conclusions References
Propane
Atmospheric
Earth
Giant planets
Spectroscopy of propane
Absorption cross sections
Experimental
Canadian light source (CLS)
Spectrometer and cell
Conditions
Results
Data processing
Cross sections
Reference data
Integrated areas
Conclusions
Future work
References
Acknowledgments

3. Why propane?

4. Why propane? Natural Oceans, volcanoes1 Microorganisms www.nasa.gov
1Etiope & Ciccioli 2009

5. Why propane? Natural Anthropogenic Oceans, volcanoes1 Microorganisms
Biomass burning
Oil and natural gas
Combustion
1Etiope & Ciccioli 2009

6. Why propane? Natural Anthropogenic Tropospheric O3 Oceans, volcanoes1
Microorganisms
Anthropogenic
Biomass burning
Oil and natural gas
Combustion
Tropospheric O3
Oxidation via ·OH2,3
Acetone and acetaldehyde
Peroxyacetyl nitrate
Catalyzed by NOx
1Etiope & Ciccioli 2009; 2Rosado-Reyes et al. 2007; 3Singh et al. 1994

7. Why propane?

8. Why propane? Hydrocarbons Photoionization of methane4
4De La Haye et al. 2008

9. Why propane? Hydrocarbons Observations Photoionization of methane4
Abundances
4De La Haye et al. 2008

10. Why propane? Hydrocarbons Observations Databases
Photoionization of methane4
Observations
Abundances
Databases
HITRAN5*, GEISA6, PNNL7
4De La Haye et al. 2008
5Rothman et al. 2013
6Jacquinet-Husson et al. 2016
7Sharpe et al. 2004

11. Spectroscopy

12. Spectroscopy Equilibrium C2v symmetry 11 atoms
27 unique vibrational modes
7 vibrational levels <1000 cm-1
webbook.nist.gov

13. Spectroscopy Equilibrium C2v symmetry Hot bands 11 atoms Line density
27 unique vibrational modes
7 vibrational levels <1000 cm-1
Hot bands
Line density
Spectral complexity
Perturbations
webbook.nist.gov

14. Spectroscopy Equilibrium C2v symmetry Hot bands 11 atoms Line density
27 unique vibrational modes
7 vibrational levels <1000 cm-1
Hot bands
Line density
Spectral complexity
Perturbations
webbook.nist.gov
8Harrison & Bernath 2010

15. Spectroscopy Equilibrium C2v symmetry Hot bands Arduous analysis
11 atoms
27 unique vibrational modes
7 vibrational levels <1000 cm-1
Hot bands
Line density
Spectral complexity
Perturbations
Arduous analysis
E.g. Perrin et al.9
9Perrin et al. 2015
webbook.nist.gov

16. Spectroscopy Equilibrium C2v symmetry Hot bands Arduous analysis
11 atoms
27 unique vibrational modes
7 vibrational levels <1000 cm-1
Hot bands
Line density
Spectral complexity
Perturbations
Arduous analysis
E.g. Perrin et al.9
Absorption cross sections
9Perrin et al. 2015
webbook.nist.gov

17. Absorption cross sections
𝜎(𝜈,𝑇)=−𝜉 𝑘 𝐵 𝑇 𝑃𝑙 ln 𝜏(𝜈,𝑇) 8
s = Absorption cross section (cm2 molecule-1)
n = Frequency (cm-1)
T = Temperature (K)
kB = Boltzmann constant (J K-1)
P = Pressure (Pa)
l = Optical path length (m)
t = Transmittance
x = Calibration factor
8Harrison & Bernath 2010

18. Absorption cross sections
𝜎(𝜈,𝑇)=−𝜉 𝑘 𝐵 𝑇 𝑃𝑙 ln 𝜏(𝜈,𝑇) 8
s = Absorption cross section (cm2 molecule-1)
n = Frequency (cm-1)
T = Temperature (K)
kB = Boltzmann constant (J K-1)
P = Pressure (Pa)
l = Optical path length (m)
t = Transmittance
x = Calibration factor
Physical parameters
Pressure
Optical path length
Temperature
9Harrison & Bernath 2010

19. Absorption cross sections
𝜎(𝜈,𝑇)=−𝜉 𝑘 𝐵 𝑇 𝑃𝑙 ln 𝜏(𝜈,𝑇) 8
s = Absorption cross section (cm2 molecule-1)
n = Frequency (cm-1)
T = Temperature (K)
kB = Boltzmann constant (J K-1)
P = Pressure (Pa)
l = Optical path length (m)
t = Transmittance
x = Calibration factor
Physical parameters
Pressure
Optical path length
Temperature
Direct information
Peak intensities
Comparison
9Harrison & Bernath 2010

20. Absorption cross sections
𝜎(𝜈,𝑇)=−𝜉 𝑘 𝐵 𝑇 𝑃𝑙 ln 𝜏(𝜈,𝑇) 9
s = Absorption cross section (cm2 molecule-1)
n = Frequency (cm-1)
T = Temperature (K)
kB = Boltzmann constant (J K-1)
P = Pressure (Pa)
l = Optical path length (m)
t = Transmittance
x = Calibration factor
Physical parameters
Pressure
Optical path length
Temperature
Direct information
Peak intensities
Comparison
Straightforward
No transition assignment
No fitting of molecular constants
9Harrison & Bernath 2010

21. Experimental Canadian Light Source Far-IR beamline
Bruker IFS 125 spectrometer
2 m White-type cell
Methanol cooled to 200 K

22. Experimental Canadian Light Source Far-IR beamline
Bruker IFS 125 spectrometer
2 m White-type cell
Methanol cooled to 200 K

23. Experimental Canadian Light Source 32 conditions Far-IR beamline
Bruker IFS 125 spectrometer
2 m White-type cell
Methanol cooled to 200 K
32 conditions
Temperature: 298, 260, 230 and 200 K
Pressure: Pure, 8*, 30* or 100* Torr
*Total pressure
Broadener: H2 or He
Sample scans and backgrounds
300 each

24. Results – Data processing
E.g Torr propane broadened to 8 Torr with H2 at 292 K
OPUS 6.010
Record pairs of interferograms
Fourier transform
Blackman-Harris 3-Term apodization function
Zero-fill factor of at least 8
Weighted averages
Sample single channel
Scaled background
Calculate transmittance spectrum
10OPUS 2006

25. Results – Data processing
E.g Torr propane broadened to 8 Torr with H2 at 292 K
OPUS 6.010
Record pairs of interferograms
Fourier transform
Blackman-Harris 3-Term apodization function
Zero-fill factor of at least 8
Weighted averages
Sample single channel
Scaled background
Calculate transmittance spectrum
Obtain absorption cross section
𝜎(𝜈,𝑇)=−𝜉 𝑘 𝐵 𝑇 𝑃𝑙 ln 𝜏(𝜈,𝑇) 9
Excel, MATLAB, Python …
10OPUS 2006

26. Results – Cross sections
Pressure dependence
Decreased peak intensities
Broadening
*near 700 cm-1 at 200 K
P (Torr)
Full-width half maximum (cm-1)*
Resolution (cm-1) H2 He
Pure
0.002 8
0.010
0.005 30
0.035
0.029
100
0.10
0.096
0.040
11Wong et al. 2017

27. Results – Cross sections
Pressure dependence
Decreased peak intensities
Broadening
*near 700 cm-1 at 200 K
Pseudo continuum
292 K
P (Torr)
Full-width half maximum (cm-1)*
Resolution (cm-1) H2 He
Pure
0.002 8
0.010
0.005 30
0.035
0.029
100
0.10
0.096
0.040
11Wong et al. 2017

28. Results – Cross sections
Temperature dependence
Increased peak intensities
Different populations
Doppler width
11Wong et al. 2017

29. Results – Cross sections
Temperature dependence
Increased peak intensities
Different populations
Doppler width
E.g. Total P(propane + H2) = 8 Torr
11Wong et al. 2017

30. Results – Reference data
Pacific Northwest National Laboratory (PNNL)7
Propane broadened with N2
Warm temperatures
278, 298 and 323 K
“Full” spectrum
600 – 6500 cm-1
7Sharpe et al. 2004

31. Results – Reference data
Pacific Northwest National Laboratory (PNNL)7
Propane broadened with N2
Warm temperatures
278, 298 and 323 K
“Full” spectrum
600 – 6500 cm-1
Conversion
ppm-1 molecule-1 to cm2 molecule-1
𝐹= 𝑘 𝐵 𝑇𝑙𝑛(10)
× 10-16
T = 296 K
7Sharpe et al. 2004

32. Results – Integrated areas
Area is retained
Temperature and pressure
Pseudo continuum

33. Results – Integrated areas
Area is retained
Temperature and pressure
Pseudo continuum
𝑦 𝑥 𝜎 𝐶𝐿𝑆 𝑑𝜈≈ 𝑦 𝑥 𝜎 𝑃𝑁𝑁𝐿 𝑑𝜈
x = 680 cm-1
y = 970 cm-1
6.588×10-19 cm molecule-1
Within 10%
Accuracy
P and l

34. Results – Integrated areas
T (K)
Pure
8 Torr H2
30 Torr H2
100 Torr H2 P
Peff
200 --
0.200
0.198
0.576
0.613
230
0.238
0.226
0.231
0.763
0.820
1.220
1.215
260
0.307
0.286
0.438
0.389
0.798
0.827
1.097
1.080
292
0.329
0.317
0.535
0.506
0.869
1.300
1.271
Area is retained
Temperature and pressure
Pseudo continuum
𝑦 𝑥 𝜎 𝐶𝐿𝑆 𝑑𝜈≈ 𝑦 𝑥 𝜎 𝑃𝑁𝑁𝐿 𝑑𝜈
x = 680 cm-1
y = 970 cm-1
6.588×10-19 cm molecule-1
Within 10%
Accuracy
P and l
T (K)
Pure
8 Torr He
30 Torr He
100 Torr He P
Peff
200 --
0.201
0.197
0.568
0.556
1.200
1.238
230
0.240
0.239
0.232
0.224
0.800
0.859
1.264
260
0.304
0.315
0.443
0.426
0.786
0.730
1.101
1.115
292
0.345
0.296
0.546
0.559
0.868
0.855
1.303
1.286

35. Conclusions Synchrotron radiation Absorption cross sections
Higher signal-to-noise-level
Higher flux
Absorption cross sections
Far-IR region
From 200 – 292 K
Pure, 8 Torr, 30 Torr and 100 Torr
Either H2 or He
Validate accuracy
PNNL database
Integrated s(n, T)

36. Conclusions Synchrotron radiation Absorption cross sections
Higher signal-to-noise-level
Higher flux
Absorption cross sections
Far-IR region
From 200 – 292 K
Pure, 8 Torr, 30 Torr and 100 Torr
Either H2 or He
Validate accuracy
PNNL database
Integrated s(n, T)
Publications
J. Quant. Spectrosc. Radiat. Transfer,
Mol. Astrophys.,
Current and future work
Propane
Even colder temperatures (150 K)
Higher frequency region (3 mm)
Other small hydrocarbons
Ethane
Propene

37. Acknowledgements Old Dominion University Dr. R.J. Hargreaves CLS
Bernath Group
Dr. R.J. Hargreaves
Oxford University
CLS
Dr. B.E. Billinghurst

38. References 1Etiope, G., Ciccioli, P., Science, 2009, 323, 478.
2Rosado-Reyes, C.M., et al., J. Geophys. Res., 2007, 112, D14310.
3Singh, H.B., et al., J. Geophys. Res., 1994, 99, 1805.
4De La Haye, V., et al., Icarus, 2008, 197, 110.
5Rothman, L. S. et al., J. Quant. Spectrosc. Radiat. Transfer, 2013, 130, 4.
6Jacquinet-Husson, et al., J. Mol. Spectrosc., 2016, 327, 31.
7Sharpe, S.W., et al., Appl. Spectrosc., 2004, 58, 1452.
8Harrison, J.J., Bernath, P.F., J. Quant. Spectrosc. Radiat. Transfer, 2010, 111, 1282.
9Perrin, A., et al., J. Mol. Spectrosc., 2015, 315, 55.
10OPUS Version 6.0, Build: 6, 0, 72 ( ) Copyright © Bruker Optik GmbH.
11Wong, A., et al., J. Quant. Spectrosc. Radiat. Transfer, 2017, 198, 141.
12Wong, A., et al., Mol. Astro., 2017, 8, 36.