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Andy Wong Robert J. Hargreaves Peter F. Bernath Michaël Rey Vladimir G. Tyuterev Infrared spectroscopy of methane: Empirical line lists within the 1-2 mm region
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Methane Atmospheric Production Greenhouse gas Fossil fuels
GWP = 34 over 100 yrs 12.4 yr lifetime Production Fossil fuels Livestock farming Landfill
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Methane - properties Atmospheric Production Astrophysical
Greenhouse gas GWP = 34 over 100 yrs 12.4 yr lifetime Production Fossil fuels Livestock farming Landfill Astrophysical Solar system Jupiter and Titan Sub-stellar environments Hot Jupiters Exoplanets Brown Dwarfs Computational modelling Quantum number assignment Spectral prediction
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Methane - properties Atmospheric Production Astrophysical
Greenhouse gas GWP = 34 over 100 yrs 12.4 yr lifetime Production Fossil fuels Livestock farming Landfill Astrophysical Solar system Jupiter and Titan Sub-stellar environments Hot Jupiters Exoplanets Brown Dwarfs Computational modelling Quantum number assignment Spectral prediction
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Methane - properties Exoplanets/ Brown Dwarfs Planets M Dwarf Stars
The Sun K (e.g., CN, OH, CH, NH) Sunspots K (e.g., H2O, TiO) EARTH – 296 K HITRAN database HITEMPA Exoplanets/ Brown Dwarfs Planets M Dwarf Stars Stars H2O NH3 CH4 8000 7000 6000 5000 4000 3000 2000 1000 Diatomic Molecules H+ Polyatomic Molecules
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Methane - properties Spectroscopic IR active fundamental
Td symmetry IR active fundamental vibrations have T2 symmetry Bands appear as polyads n1 n2 n3 n4 3025 cm-1 1583 cm-1 3157 cm-1 1367 cm-1
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Methane - properties Spectroscopic IR active fundamental
Td symmetry IR active fundamental vibrations have T2 symmetry Bands appear as polyads A. Nikitin et al. PCCP, 2013, 15, 10071 n1 n2 n3 n4 3025 cm-1 1583 cm-1 3157 cm-1 1367 cm-1
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Experimental Spectrometer Scans Tube furnace InSb detector
CaF2 windows 0.02 cm-1 resolution Quartz-halogen source Scans 600 per sample 600 per background Tube furnace Between K 100 Torr of CH4
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Experimental Spectrometer Scans Tube furnace InSb detector
CaF2 windows 0.02 cm-1 resolution Scans 600 per sample 600 per background Tube furnace Between K 100 Torr of CH4
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spectra
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Empirical Lower state energies
Pick line lists Calibrate to HITRAN Frequency Intensity
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Empirical Lower state energies
Pick line lists Calibrate to HITRAN Frequency Intensity Beer-Lambert Law Line strength 𝜏=𝐼/ 𝐼 0 =exp − 𝑺 ′ 𝑔 𝜈− 𝜈 0 𝑵𝒍 𝑺 ′ = 2 𝜋 2 𝝂 𝑺 𝑱 ′ 𝑱 ′′ 3 𝜀 0 ℎ 𝑐 𝑸 𝑻 exp − 𝑬 ′′ 𝑘𝑻 1− exp − ℎ𝝂 𝑘𝑻
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Empirical Lower state energies
“8-temperature method” “2-temperature method” A. Campargue et al. JQSRT, 2013, 118 𝑆 ′ 𝑆 0 ′ = 𝑄 0 𝑄 exp 𝑬 ′′ 𝑘 𝑇 0 − 𝑬 ′′ 𝑘𝑇 1− exp − ℎ𝜈 𝑘𝑇 1− exp − ℎ𝜈 𝑘 𝑇 0
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Empirical Lower state energies
Tetradecad Icosad Triacontad
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Empirical Lower state energies - Tetradecad
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Computational modelling
M. Rey et al. Variational ab initio Irreducible tensor operators Exploit symmetry Reduce size of Hamiltonian Rotational structure Vibrational fitting Accurate line positions and intensities Evaluation at 298 K A. V. Nikitin et al. PCCP, 2013, 15
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Theory vs Experiment (298 K)
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Theory vs Experiment (298 K)
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Quantum Number assignment
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Quantum Number assignment
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Conclusions and future work
Hot CH4 298 to 1000K Empirical line lists Lower state energies Variational ab initio M. Rey et al. QN assignment ~2000 transitions in tetradecad band Further assignments Icosad and Triacontad Elevated temperatures Direct comparison to observation
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acknowledgments Spectroscopy group at ODU Theoretical group at Reims
Peter F. Bernath Robert J. Hargreaves (Oxford) Christopher Beale Mike Dulick Theoretical group at Reims Michaël Rey Andrei V. Nikitin Vladimir G. Tyuterev
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