The ν 1  + ν 5 high resolution infrared band of FClO 3.

The high resolution infrared spectra of the mono isotopic species F35Cl16O3, F37Cl16O3, F35Cl18O3 and F37Cl18O3 have been analysed in the region of the ν1 + ν5 perpendicular combination band, from 1540 to 1680 cm−1. For all the isotopologues the ν1 + ν5 band is of medium intensity at the recording conditions. In total, about 2400, 2000, 2600 and 2700 transitions have been assigned for F35Cl16O3, F37Cl16O3, F35Cl18O3 and F37Cl18O3, respectively. The data for each band have been analysed on the basis of the usual Hamiltonian for a degenerate state of a molecule of C3v symmetry. In addition, two interaction terms have been considered active within the v1 = v5 = 1 state, with and selection rules. The ro-vibration parameters of the v1 = v5 = 1 states have been obtained, together with the band origins. Combining the ν1 + ν5 origins with those of the ν1 and ν5 fundamentals, the anharmonicity constant has been derived for the four molecules and compared to the corresponding value calculated ab initio. [ABSTRACT FROM PUBLISHER]