Water vapour spectroscopy in the MSF Dr Robert McPheat CAVIAR Progress Meeting NPL 02/06/2008

SPAC Short path-length absorption cell (SPAC) –1.2 to 20 metres –Multi-pass reflective optics (White) –Being upgraded for CAVIAR -200 to 200ºC temperature range 5 bar maximum pressure No cold spots (including valves, feedthroughs etc.) Mirrors adjustable from outside Accurate temperature & humidity measurement Corrosion resistant Made first measurements Problems with thermal expansion –Can be used for hot measurements

SPAC upgrade OpticsInnerCooling Jacket

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

SPAC upgrade modifications

Second High Resolution Spectrometer Bruker IFS120 HR Upgrade –Upgraded electronics / moving mirror to same specification as IFS125 –Maximum spectral resolution of cm -1 –Spectral range of 10 to 40,000 cm -1

LPAC Vacuum Upgrades Replace unreliable pumps & gauges (dating from early 1970s) Oil free to avoid contamination –3 large dry pumps –1 dry backing pump –6 new gauges

Future Work Measurement of unsaturated strong lines Finish SPAC modifications –Measurements covering visible to FIR Need window & detector box modifications for FIR –Up to 450 K LPAC vacuum upgrade –Measurement conditions –243K to 293K –water pressures up to 0.75 SVP –resolution up to possible cm -1 but mainly at 0.03cm -1 –water/air mixtures at total pressures of 150, 500 & 1000 hPa