The 2ν4 overtone bands of F35Cl16O3

The high resolution infrared spectrum of the mono-isotopic species F35Cl16O3 has been studied in the region of the 2ν4 overtone, from 2560 to 2680 cm−1. The 2ν4∓2 perpendicular component is strong and clearly observed while the 2ν40 parallel component is very weak and almost completely hidden by the perpendicular one. Their origins differ by 12.6 cm−1, the 2ν4∓2 being located at higher wavenumbers. The 2ν4∓2 band is perturbed by the anharmonic interaction between the v4 = 2, l4 = ∓2 and v2 = v4 = v5 = 1, l4 = l5 = ±1 excited states, both of E symmetry. In total 3157 transitions have been assigned, 83% of these to 2ν4∓2, 12% to ν2+ν4±1+ν5±1, and 5% to 2ν40. The three bands have been analyzed simultaneously, taking into account the Fermi resonance effective between the excited states of E symmetry. The ro-vibration parameters of the excited states have been obtained, including the deperturbed band origins of 2ν4∓2 and ν2+ν4±1+ν5±1, at 2628.5890(4) and 2619.3342(5) cm−1, respectively. The W245 anharmonic constant is equal to 4.0161(4) cm−1. The x44+g44 and x24+x45+g45 anharmonicity constants have been derived from the obtained band origins and those of ν4 and ν2 + ν5.