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

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

Why propane? www.nasa.gov

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

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

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 www.nasa.gov 1Etiope & Ciccioli 2009; 2Rosado-Reyes et al. 2007; 3Singh et al. 1994

Why propane? www.nasa.gov

Why propane? Hydrocarbons Photoionization of methane4 4De La Haye et al. 2008 www.nasa.gov

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

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 www.nasa.gov

Spectroscopy

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

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

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

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

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

Absorption cross sections 𝜎(𝜈,𝑇)=−𝜉 10 4 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

Absorption cross sections 𝜎(𝜈,𝑇)=−𝜉 10 4 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

Absorption cross sections 𝜎(𝜈,𝑇)=−𝜉 10 4 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

Absorption cross sections 𝜎(𝜈,𝑇)=−𝜉 10 4 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

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

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

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

Results – Data processing E.g. 0.54 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

Results – Data processing E.g. 0.54 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 10 4 𝑘 𝐵 𝑇 𝑃𝑙 ln 𝜏(𝜈,𝑇) 9 Excel, MATLAB, Python … 10OPUS 2006

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 0.00096 8 0.010 0.005 30 0.035 0.029 100 0.10 0.096 0.040 11Wong et al. 2017

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 0.00096 8 0.010 0.005 30 0.035 0.029 100 0.10 0.096 0.040 11Wong et al. 2017

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

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

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

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 4 0.101325 9.28697 × 10-16 T = 296 K 7Sharpe et al. 2004

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

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

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

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)

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, 201711 Mol. Astrophys., 201712 Current and future work Propane Even colder temperatures (150 K) Higher frequency region (3 mm) Other small hydrocarbons Ethane Propene

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

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