Knowledge Bank

Spectra of $\mathrm{<mrow\; data-mjx-texclass="ORD">18</mrow>}$O-enriched ozone samples have been recorded around 10 $\mu m$ with a resolution of $0.005cm-1$ using the McMath Fourier transform interferometer. Different isotopic mixtures have been used to facilitate the assignment of the spectra : with an excess of oxygen 16, the main absorbing species are $\mathrm{<mrow\; data-mjx-texclass="ORD">16</mrow>}O,16O16O18O$ (noted 668) and $\mathrm{<mrow\; data-mjx-texclass="ORD">16</mrow>}O18O16O$ (noted 686) whereas with an excess of oxygen 18 the main absorbers are $\mathrm{<mrow\; data-mjx-texclass="ORD">18</mrow>}O,18O18O16$ and $\mathrm{<mrow\; data-mjx-texclass="ORD">18</mrow>}O16O18$. The spectrum of normal ozone being now well known, we have concentrated our attention on the study of the spectra of the two isotopic species 668 and 686. The 686 molecule belongs to the $C2v$ point group and consequently the structure of the observed bands (i.e. $\nu 3$ and $\nu 1$ ) is the same as for $\mathrm{<mrow\; data-mjx-texclass="ORD">16</mrow>}O3$. On the contrary 668 belongs to the $Cs$ point group and $\nu 3$ and $\nu 1$ are hybrid bands having A-and B-type components. Due to the number of isotopic species, it was rather difficult to start the analysis. In fact, we managed to begin the analysis using both series of lines and ground state combination differences. Then, with the help of the ground state rotational constants known from microwave studies, we have obtained upper levels which were introduced in a least-squares fit leading to the determination of a first set of rotational and coupling constants which then were used to calculate extrapolated line positions allowing new assignments. This process was repeated until all the lines were assigned. For both molecules the $\nu 3$ A-type band is the stronger and the easiest to assign. For 686 it has been possible to locate lines of the much weaker $\nu 1$ band (B-type). For 668 the $\nu 1$ band is mainly of A-type (the B-type $\nu 1$ band is hardly visible). This $\nu 1$ A-type band has a strong and narrow Q branch around $1090cm-1$ resulting from the superposition of more than 200 single lines. This Q branch is clearly visible in spectra of the earth’s atomosphere. For 686 the rotational energy levels of the (001) and (100) states were reproduced within their experimental error ($0.0005cm-1$) taking into account the Coriolis interaction. For 668, both Fermi and Coriolis type interactions were necessary to reproduce correctly the experimental levels. Several line intensities of both isotopic species were measured leading to the determination of the transition moment operators of the observed bands.