Assignment of lines
As many impurities are present in ozone spectra, due to its large reactivity, we may observe H2O,
N2O, CO, CO2 and HNO3 lines.
The situation is relatively easy in case of 16O3 spectra, as the positions and intensities
of the main isotopes of these molecules are reported in databases as HITRAN or GEISA. In this case, we fit only the
partial pressure of various gases in the observation cell.
Note that a constant correction to air-broadening coefficient is applied to air-broadening coefficient of databases.
This allows to take account of the variation of this coefficient with rotational quantum number. The self-broadening
coefficient does not play any role, as partial pressures of impurities are lower than 1 Torr. These pressures are
reported into section "Spectra". For the positions and intensities of v2 H216O
band, we used updated data of R.A. Toth, J.Opt.Soc.Am.B, Vol.8, No.11, 2236-2255 (November 1991).
Unfortunately the situation is a little more complicated for 18O enriched impurities which are not
so well known or absent in databanks (HN18O3 as example).
This part is in relation with theory. Let us just give some remarks. As far as potential function is precise, we have
available predictions for band centers and rotational constants for excited studied states. This allows to perform a
preliminary calculation of transitions. If the bands are strong enough (but not saturated) and if not too much impurities
are present a code for assignments (ASSIGN) described in A. Chichery thesis (Reims, France, 2000) allows to assign some
transitions and to start with the well known procedure of successive fits and assignments. The situation is obviously much
more complicated for weak bands, mostly B type, where often only one type of transition appears. In this case, and mostly
when "dark states" are involved, the procedure of assignments may be very long and not straightforward.