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Progress in water vapour spectroscopy at RAL

Progress in water vapour spectroscopy at RAL. Dr Robert McPheat CAVIAR Progress Meeting Cosners’ House, 14/12/2009. Measurements in the mid- and near-IR. These measurements were intended to target the weak water vapour continuum. Long path lengths.

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Progress in water vapour spectroscopy at RAL

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  1. Progress in water vapour spectroscopy at RAL Dr Robert McPheat CAVIAR Progress Meeting Cosners’ House, 14/12/2009

  2. Measurements in the mid- and near-IR. These measurements were intended to target the weak water vapour continuum. Long path lengths. Measurements carried out at moderate (0.01cm-1) & high resolution (0.002cm-1) using the Bruker IFS125 HR. Initial measurements revealed a need for better line data too. Previous MSF Measurements

  3. Water line parameter measurements • Although CAVIAR is targeted at improving the water vapour continuum, errors in line parameters contribute to the measured continuum • First measurements with upgraded Bruker IFS120 HR • Upgraded electronics / moving mirror to same specification as IFS125 • High resolution measurements 0.002 cm-1 • Long integration times (~ 12 hours) in mid-IR

  4. 5 mm Cell • 5 mm path length • Electropolished stainless steel for low surface adsorption • Spherical reservoir volume to increase volume to surface ratio • All metal vacuum system • Parylene coated KBr windows attached with low vapour pressure epoxy resin

  5. 5 mm Cell

  6. 5 mm Cell

  7. Water line parameter measurements • 486 measurements covering mid & near IR • Up to 13 hPa pure water • Room temperature • Spectra, temperature & pressure measurements delivered to Reading for analysis

  8. Mid-IR Spectra Wavenumber /cm-1 1250 2000

  9. Mid-IR Spectra Wavenumber /cm-1

  10. Near-IR Spectra 1600 6000 Wavenumber /cm-1

  11. Near-IR Spectra Wavenumber /cm-1

  12. SPAC upgrade Optics Inner Cooling Jacket

  13. High temperature pressure gauge & filling line Electrical feedthroughs Temperature & pressure logging Temperature control Outer vacuum jacket Detector box Transfer optics vacuum tank

  14. SPAC upgrade modifications • Additional base heaters added • Inner modified to avoid problems with thermal expansion

  15. Example Spectra 420 – 450 K Up to 1 bar water vapour Up to 5 bar total pressure Wavenumber /cm-1 1800 11000

  16. SPAC upgrade problems • Problems with water condensation on bottom mirror • Degradation of mirror surfaces • Move feedthrough to bottom of cell • Will also solve wiring problems • Replace thin film heaters • Kapton wires • More PRTs • Remove humidity sensors • Replace O ring • Simplify connections

  17. Electrical feedthroughs Electrical feedthroughs for PRTs moved to bottom of the cell produce a much simplified vacuum / pressure system

  18. Example Spectra at 160 °C Background 3000 hPa Water vapour 1600 Wavenumber / cm-1 12000

  19. Self Broadened Spectra 100 % 3000 hPa Water vapour at 160 °C Transmittance 2000 Wavenumber / cm-1 11000

  20. Air Broadened Spectra Example Spectra 100 % 600 mbar water vapour in 5 bar total pressure mixture with air at 160 deg. C 2500 Wavenumber / cm-1 10000

  21. Further work • Further NIR SPAC spectra • Extend SPAC measurements towards visible • MIR SPAC measurements up to 1.5 bar • MIR LPAC measurements

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