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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. - PowerPoint PPT Presentation
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Progress in water vapour spectroscopy at RAL
Dr Robert McPheat
CAVIAR Progress Meeting
UCL, 13/05/2010
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
High temperature pressure gauge & filling line
Temperature & pressure logging
Temperature control
Outer vacuum jacket
Transfer optics vacuum tank
Detector box
Electrical feedthroughs
Example SpectraAir Broadened Spectra
600 mbar water vapour in 5 bar total pressure mixture with air at 160 deg. C
100 %
2500 Wavenumber / cm-1 10000
Pure H2O measurements (self-continuum):
1) empty cell2) 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 cell2) Air (5 atm)3) Air + H2O (5 atm total)
4) Same as in 2)5) empty cell
SPAC measurement procedure
F Foreign (H2O + Air; 5atm total pressure) measurements, in addition to the
pure H2O
(F)Only foreign (5 atm total pressure) measurementAll air broadened measurements 0.1 cm-1.
Near-IR SPAC measurements
Saturated PH2O
(mb) !
T (K) PH2O (mb)
35 300 20(F)
416 350 50(F), 300F
1000 375 50(F), 400, 600F, 750
2500 400 600F, 1000, 1500F, 2000
5700 430 600F, 1000, 1500, 2000, 3000, 4000
14000 470 1000, 2000, 3000, 4000, 5000
Resolution (cm-1):
N of scans:
0.05 0.1 0.2 : 0.3
1000 500
2000 – 10000 cm-1, 5 – 1 µm
Saturated PH2O
(mb)!
T (K) PH2O (mb)
416 350 300F
1000 375 300(F) 750
2500 400 300(F) 1000, 1500
5700 430 1000, 1500 2000, 3000, 4000
14000 470 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 (H2O + Air; 5atm total pressure) measurements, in addition
to the pure H2O
(F) Only foreign (5 atm total pressure) measurement
Near-visible SPAC measurements
8500 – 14000 cm-1, 1.18 – 0.714 µm
SPAC reconfiguration
• Measure pathlength
• Install BaF2 windows
• Maximum pressure 1.5 bar
• ~ 800 cm-1 long wavelength cut off.