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New line intensities for the far infrared bands of the Trans- and Cis-conformer of nitrous acid (HONO), new determination of the Trans-Cis conformer barrier and its impact on the astrophysical detection of nitrous acid in protostellar clouds

par Betnga, Tchana;Kwabia-Tchana, Fridolin;Perrin, Agnès;Manceron, Laurent;Vander Auwera, Jean ;Hindle, F.;Coutens, A.
Référence Journal of quantitative spectroscopy & radiative transfer, 310, page (108727)
Publication Publié, 2023-01-01

Article révisé par les pairs

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Résumé :

The first goal of this work is to improve the determination of the energy difference (ΔECis-Trans) between the ground vibrational state of the Cis- and Trans-HONO conformers of nitrous acid. For this, high resolution spectra were recorded in the 50–200 cm−1 spectral region at three different temperatures, 240, 270 and 296 K. The relative line intensities for the B-type transitions of pure rotational bands of Trans-HONO and Cis-HONO achieved from our measurements were combined in least squares fit computations to those measured previously by Sironneau et al. [Sironneau V, Flaud JM, Orphal J, Kleiner I, Chelin P. Absolute line intensities of HONO and DONO in the far-infrared and re-determination of the Energy Difference between the trans- and cis-species of nitrous acid. J Mol Spectrosc 2010;259:100–104]. In this way, we can significantly improve the accuracy on the HONO conformer energy difference, with a value for ΔECis-Trans = 95.8 ± 9.2 cm−1 compared to SIRΔECis-Trans = 99 ± 25 cm−1 in the previous study of Sironneau et al. The second goal is to generate a line list with “absolute” line intensities for the pure rotational bands in the far infrared region of Trans-HONO and Cis-HONO, with both A- and B-type transitions. This new line list proved to be more robust for an improved detection of HONO in astrophysical objects [Coutens A, Ligterink NFW, Loison JC, Wakelam V, Calcutt H, Drozdovskaya MN, Jørgensen JK, Müller HSP, Van Dishoeck EF, Wampfler SF. The ALMA-PILS survey: First detection of nitrous acid (HONO) in the interstellar medium. Astronomy & Astrophysics 2019;623:L13].