Spectroscopy and predissociation of the 3A2 electronic state of ozone 16O3 and 18O3 by high resolution Fourier transform spectrometry

Abstract A high resolution Fourier transform spectrometry analysis of the rotational structure of the 2 0 1 absorption bands of the 3 A 2 ← X 1 A 1 Wulf transition for the isotopomers 16 O 3 and 18 O 3 of the ozone molecule is presented. These bands are very intense compared to the 0 0 0 bands but the predissociation is so strong that the main sub-bands appear as continuous contours. Isolated lines and band contour methods are used together to analyse these two rovibrational bands. The lines corresponding to the F 2 component are generally the most intense and isolated. Our data sets for the (0 1 0) level of the 3 A 2 state are limited to about 102 weakly or unperturbed rotational lines for the 2 0 1 of 16 O 3 in the range 9620–10 140 cm −1 and 123 weakly or unperturbed rotational lines for the same band of 18 O 3 . Using for each of them the well-defined ground state parameters, we obtained a standard deviation of about 0.035 cm −1 in the fit to the lines for 16 O 3 and 0.027 cm −1 in the case of 18 O 3 . The rotational constants A , B and C , the three rotational distortion terms Δ K , Δ JK and Δ J , the spin–rotation constants a 0 , a and b have been successfully calculated for 16 O 3 and 18 O 3 while the spin–spin constants were fixed to their respective values obtained for the origin bands. As is the case for the 0 0 0 band, we have a partial agreement with the isotopic laws for the rotational constants. The geometrical parameters of the (0 1 0) level of 3 A 2 state for the two isotopomers are close, r =1.357 A, θ =100.7° for 18 O 3 and r= 1.352 A and θ =100.0° for 16 O 3 . The origin of the 2 0 1 band of 18 O 3 is red shifted by 7.06(4) cm −1 with respect to 16 O 3 2 0 1 band and the two bending mode quanta are, respectively, 528.99(9) and 501.34(7) cm −1 . A preliminary qualitative analysis of the predissociation is given in the particular case of the F 2 spin component of 16 O 3 for 0 0 0 and 2 0 1 bands by the measurement of shifts of positions of some rovibrational levels and the evolution of predissociation broadenings in Q Q 2 branches. We justify the existence of perturbations in the rovibrational levels of 3 A 2 state through different interaction types: with the dissociation continuum of the same electronic state or with high vibrational repulsive or weakly bound levels of the ground state.