Progress in water vapour spectroscopy at ral
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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.

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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


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

Previous MSF Measurements


Progress in water vapour spectroscopy at ral

SPAC

White Optics

Inner

Cooling Jacket


Progress in water vapour spectroscopy at ral

High temperature pressure gauge & filling line

Electrical feedthroughs

Temperature & pressure logging

Temperature control

Outer vacuum jacket

Detector box

Transfer optics vacuum tank


Progress in water vapour spectroscopy at ral

Example Spectra at 160 °C

Background

3000 hPa Water vapour

1600Wavenumber / cm-1 12000


Progress in water vapour spectroscopy at ral

Self Broadened Spectra

100 %

3000 hPa Water vapour at 160 °C

Transmittance

2000Wavenumber / cm-1 11000


Progress in water vapour spectroscopy at ral

Air Broadened Spectra

Example Spectra

100 %

600 mbar water vapour in 5 bar total pressure mixture with air at 160 deg. C

2500Wavenumber / cm-1 10000


Progress in water vapour spectroscopy at ral

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


Progress in water vapour spectroscopy at ral

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.


Progress in water vapour spectroscopy at ral

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


Progress in water vapour spectroscopy at ral

SPAC reconfiguration

  • Measure pathlength

  • Install BaF2 windows

  • Maximum pressure 1.5 bar

  • ~ 800 cm-1 long wavelength cut off.


Progress in water vapour spectroscopy at ral

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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