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

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 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

3. SPAC White OpticsInnerCooling Jacket

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

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

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

7. 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

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

9. F Foreign (H 2 O + Air; 5atm total pressure) measurements, in addition to the pure H 2 O (F)Only foreign (5 atm total pressure) measurement All air broadened measurements 0.1 cm -1. Near-IR SPAC measurements Saturated P H2O (mb) ! T (K)P H2O (mb) 3530020(F) 41635050(F), 300 F 100037550(F), 400, 600 F,750 2500400 600 F,1000, 1500 F,2000 5700430 600 F,1000, 1500,2000, 3000, 4000 14000470 1000,2000, 3000, 4000, 5000 Resolution (cm -1 ): N of scans: 0.050.1 0.2 : 0.3 1000 500 2000 – 10000 cm -1, 5 – 1 µm

10. Saturated P H2O (mb)! T (K)P H2O (mb) 416350 300 F 1000375 300(F)750 2500400 300(F)1000, 1500 57004301000, 15002000, 3000, 4000 14000470 4000, 5000 Resolution (cm -1 ): N of scans: 0.05 (0.2 foreign) 0.1 | 0.2 (0.2 foreign) 0.2 | 0.3 -> 500 F Foreign (H 2 O + Air; 5atm total pressure) measurements, in addition to the pure H 2 O (F) Only foreign (5 atm total pressure) measurement Near-visible SPAC measurements 8500 – 14000 cm -1, 1.18 – 0.714 µm

11. SPAC reconfiguration Measure pathlength Install BaF 2 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 Saturated P H2O (mb) ! T (K)P (mb) 13.8285 ? 10 F 19.1290 10, 15 F 27.8296 20(F) 10, 15 F, 20 62310 50 20(F) No Argon steps are needed for LPAC measurements 135325 100 20(F) 270340 100, 150, 200 510355 100, 150, 200, 350 Resolution (cm -1 ): N of scans: 0.01 0.02 | 0.050.003 ? (to ensure good S/N) | SPAC, 20m | LPAC, 512m (F) Only foreign measurement: H 2 O + Air( 1.5atm) F Foreign measurement: H 2 O + Air( 1.5atm), in addition to the pure one