High-resolution analysis of the 12.6 µm spectral region of the nitryl chloride ClNO2 molecule.

Highlight • Nitryl chloride ClNO 2. • High-resolution Fourier transform spectroscopy. • First analysis of the ν 2 , 2ν 3 and 2ν 6 bands taking into account the relevant Coriolis and Fermi resonances. Abstract The 12.6 µm region of nitryl chloride (ClNO 2) has been recorded at high resolution (0.00102 cm−1) using a Fourier transform spectrometer and the SOLEIL synchrotron light source. ClNO 2 was found during our studies of chlorine nitrate and, after fractional distillations it was introduced into a multipass White cell made of inert materials, with an optical path length of 5.4 m. 320 scans were recorded for the range 600–980 cm−1 at a total pressure of 0.23 hPa and a temperature of 250 K. A thorough analysis of the ν 2 , 2ν 6 and 2ν 3 bands of 35ClNO 2 and of the ν 2 band of 37ClNO 2 falling in this region has been carried out using a Hamiltonian model which takes explicitly into account the numerous resonances affecting the ro-vibrational energy levels; especially the C-type Coriolis resonance between the ν 2 and the ν 3 + ν 6 modes. These two modes are only separated by less than 20 cm−1 and are thoroughly mixed. From the fittings, the following band centers were derived: ν o (ν 2) = 792.761264(60) cm−1, ν o (ν 3 + ν 6) = 775.8923(20) cm−1, ν o (2ν 3) = 734.183576(20) cm−1 and ν o (2ν 6) = 819.836727(90) cm−1 for 35ClNO 2 and ν o (ν 2) = 792.258284(30) cm−1 and ν o (ν 3 + ν 6) = 774.6826(30) cm−1 for 37ClNO 2 where the uncertainties are one standard deviation. Due to their sharp Q branches falling into an atmospheric "window", the detection of the ν 2 bands might be an advantageous route for future attempts to quantify atmospheric ClNO 2 , using infrared techniques. Graphical abstract Image, graphical abstract [ABSTRACT FROM AUTHOR]