The 14-22 μm absorption spectrum of nitrous acid studied by high-resolution Fourier-transform spectroscopy: New analysis of the ν5 and ν6 interacting bands of trans-HONO and first analysis of the ν6 band of cis-HONO

High-resolution Fourier-transform absorption spectra of nitrous acid (HONO) were recorded in the 400-700 cm⁻¹ spectral region. For the trans-HONO isomer a very extensive analysis of the ν₅ (ONO bend) and ν₆ (torsion) interacting fundamental bands of trans-HONO located near 595.620 and 543.879 cm⁻¹, respectively, was performed starting from the results of a previous study C.M. Deeley, I.M. Mills, L.O. Halonen, J. Kauppinen, Can. J. Phys. 63 (1985) 962-965]. In addition, for the less abundant cis-HONO isomer, the first high-resolution study of the ν₆ band located at 639.7432 cm⁻¹ was achieved, the ν₅ band is presumed to be located near 609.2 cm⁻¹. For both isomers the strong A-type and B-type Coriolis interactions linking the {5¹, 6¹} interacting energy levels were accounted for during the energy level calculations. Finally, using these results a list of positions and of realistic relative line intensities has been generated for both isomers, and a comparison with some ab initio predictions was performed.