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

2. Previous MSF Measurements 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.

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

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 12502000

9. Mid-IR Spectra Wavenumber /cm -1

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

11. Near-IR Spectra Wavenumber /cm -1

12. SPAC upgrade OpticsInnerCooling Jacket

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

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

15. Example Spectra Wavenumber /cm -1 420 – 450 K Up to 1 bar water vapour Up to 5 bar total pressure 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 for PRTs moved to bottom of the cell produce a much simplified vacuum / pressure system Electrical feedthroughs

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

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

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