Far-ir spectroscopy of ozone as a means of quantification of ozone isotopomers

The rotational spectrum of ozone in the far IR, obtained with a 0.004 cm^-1 resolution, has been used to quantify ozone isotopomers in an artificially produced mixture of normal and ¹⁸O substituted ozone species. Higher order terms in the dipole operator have been found to significantly influence the theoretical line intensities of some of the rotational transitions. A planarity relation between some of the θ-constants was found in this connection. The results have been used partly to calibrate our microwave spectrometer for future ozone isotopomer quantification and partly to quantify the mixture studied. In particular the ratio r₅₀ between unsymmetric and symmetric species of mono-¹⁸O ozone has been determined with the aim of detecting possible deviations from the statistical value 2.00; for the two mixtures studied r₅₀ = 2.12(9) and r50 = 2.00(8).