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Progress in water vapour spectroscopy at RAL

Progress in water vapour spectroscopy at RAL. Dr Robert McPheat CAVIAR Progress Meeting UCL, 13/05/2010. 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 UCL, 13/05/2010

  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 FTS. Initial measurements revealed a need for better line data too. High resolution measurements 0.002 cm-1 using the Bruker IFS120/5 HR Long integration times (~ 12 hours) in mid-IR Previous MSF Measurements

  3. SPAC White Optics Inner Cooling Jacket

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

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

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

  7. 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

  8. SPAC measurement procedure Pure H2O measurements (self-continuum): 1) empty cell 2) Argon (same pressure as H2O in step 3) 3) pure H2O (same pressure as in step 2) 4) Argon (same pressure as H2O in step 3) 5) empty cell (quick measurement) H2O + Air measurements (foreign-continuum): 1) empty cell 2) Air (5 atm) 3) Air + H2O (5 atm total) 4) Same as in 2) 5) empty cell

  9. Near-IR SPAC measurements 2000 – 10000 cm-1, 5 – 1 µm • FForeign (H2O + Air; 5atm total pressure) measurements, in addition to the pure H2O • Only foreign (5 atm total pressure) measurement • All air broadened measurements 0.1 cm-1.

  10. Near-visible SPAC measurements 8500 – 14000 cm-1, 1.18 – 0.714 µm FForeign (H2O + Air; 5atm total pressure) measurements, in addition to the pure H2O (F) Only foreign (5 atm total pressure) measurement

  11. SPAC reconfiguration • Measure pathlength • Install BaF2 windows • Maximum pressure 1.5 bar • ~ 800 cm-1 long wavelength cut off.

  12. Plan for mid-IR SPAC measurements 800 – 2100 cm-1, 12.5 – 4.8 µm | SPAC, 20m | LPAC, 512m (F) Only foreign measurement: H2O + Air(1.5atm) F Foreign measurement: H2O + Air(1.5atm), in addition to the pure one

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