Measurements of O-18-enriched ozone isotopomer abundances using high-resolution Fourier transform far-IR spectroscopy

The distribution of ozone isotopomers in ozone mixtures produced by electri c discharge in mixtures of O-16(2) and O-18(2) at 77 K was measured by high -resolution FTIR spectroscopy. It was of key importance to assess not only the total amount of isotopomers of a certain mass but also the relative amo unts of corresponding asymmetric and symmetric ozone species of the same ma ss given as the ratios [(OOO)-O-16-O-16-O-18]/[(OOO)-O-16-O-18-O-16] and [( OOO)-O-16-O-18-O-18]/[(OOO)-O-18-O-16-O-18]. For many purposes both ratios have been assumed to have the statistical value 2.00. Pure rotational spect ra in the far-IR region (30-100 cm(-1)) were recorded for three different O -18-enriched ozone mixtures, all at 0.00185 cm(-1) resolution. All the spec tra were corrected for thermal emission. Linestrengths for individual lines in a particular spectrum were measured by means of a fitting technique tak ing into account contributions from all other lines in the spectrum. For th is purpose theoretical linestrengths for all six ozone species containing O -16 and O-18. Obtained from a quantum-number-dependent dipole operator were used. The ratios between observed and theoretical linestrengths were used to determine the abundances of individual isotopomers in a particular ozone mixture. For one of the ozone samples the abundances of all six ozone spec ies were determined within 1% relative uncertainty. For the three ozone mix tures studied, the ratio between asymmetric and symmetric species of mono-O -18 ozone were determined to 1.99(2), 2.01(2), and 2.10(6). The ratio betwe en asymmetric and symmetric species of di-O-18 ozone were determined to 2.5 1(4), 2.42(10), and 2.46(3). (C) 2000 Academic Press.