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

SPAC

White Optics Inner Cooling Jacket

High temperature pressure gauge & filling line

Temperature & pressure logging

Temperature control

Outer vacuum jacket

Transfer optics vacuum tank

Detector box

Electrical feedthroughs

Example Spectra at 160 °C

Background3000 hPa Water vapour

1600 Wavenumber / cm-1 12000

Self Broadened Spectra

3000 hPa Water vapour at 160 °C

2000 Wavenumber / cm-1 11000

100 %

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.

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