Precise submillimeter-wave spectrometry of gases

The UK NPL program of submillimeter-wave absorption measurements on gases is described. The instrumentation is capable of giving absorption line centres to an absolute accuracy of ±0.003 cm⁻¹ (±100 MHz) in the spectral region 10–40 cm⁻¹ (300 GHz–1.2 THz). As well as setting standards of measurement precision at submillimeter wavelengths, the Fourier spectrometer described is being used to compile an atlas of standard spectra at these wavelengths. The results and relevance of measurements on ozone, some fréons and isotopically substituted water vapor are discussed. Examples are given of measurement capability in respect of relative and absolute intensities.