New analysis of the ν5 and ν6 interacting bands of Trans-HONO and of the ν6 band of Cis-HONO by high-resolution Fourier-transform spectroscopy in the 13–25 µm region

This article deals with the 13–25 µm bands of Trans-HONO and Cis-HONO which were already investigated in 2007 [A. Perrin, S. Miljanic, A. Dehayem-Kamadjeu, P. Chélin, J. Orphal, J. Demaison, Journal of Molecular Spectroscopy 245 (2007) 100–108] at lower resolution. The 13–25 µm HONO absorption band can potentially contribute to the observed infrared signature of the future ‘Far infrared Outgoing Radiation Understanding and Monitoring’ (FORUM) satellite instrument (https://www.forum-ee9.eu/). Using high-resolution Fourier transform spectra recorded at the SOLEIL synchrotron, we performed an extended investigation of the ν5 (ONO bend) and ν6 (torsion) interacting fundamental bands of Trans-HONO (595.620895 and 543.880143 cm−1, respectively), and of the ν6 band of Cis-HONO (639.742715 cm−1). The A- and B-type Coriolis interactions coupling the 51 and 61 energy levels were considered for both conformers, together with, , for Cis-HONO, the B-type Coriolis resonance coupling the 61 energy levels with those of 41 state (851.942928 cm−1). Finally, absolute line intensities were obtained for the ν5 and ν6 bands of both conformers by careful comparison of line intensities at 13–25 µm against those at 11 µm. For this computation, the value ΔECis-Trans = 95.8 ± 9.2 cm−1, was used for the HONO Cis- to Trans- conformers energy difference.