Discovery of the elusive carbonic acid (HOCOOH) in space ...

• Main Authors: Sanz-Novo, Miguel, Rivilla, Víctor M., Jiménez-Serra, Izaskun, Martín-Pintado, Jesús, Colzi, Laura, Zeng, Shaoshan, Megías, Andrés, López-Gallifa, Álvaro, Martínez-Henares, Antonio, Massalkhi, Sarah, Tercero, Belén, de Vicente, Pablo, Martín, Sergio, Andrés, David San, Requena-Torres, Miguel A.
• Format: Text
• Language: unknown
• Published: arXiv 2023
• Subjects: Astrophysics of Galaxies astro-ph.GA; FOS Physical sciences; Carbonic acid
• Online Access: https://dx.doi.org/10.48550/arxiv.2307.08644; https://arxiv.org/abs/2307.08644

After a quarter century since the detection of the last interstellar carboxylic acid, acetic acid (CH$_3$COOH), we report the discovery of a new one, the cis-trans form of carbonic acid (HOCOOH), toward the Galactic Center molecular cloud G+0.693-0.027. HOCOOH stands as the first interstellar molecule containing three oxygen atoms and also the third carboxylic acid detected so far in the interstellar medium. Albeit the limited available laboratory measurements (up to 65 GHz), we have also identified several pairs of unblended lines directly in the astronomical data (between 75-120 GHz), which allowed us to slightly improve the set of spectroscopic constants. We derive a column density for cis-trans HOCOOH of $N$ = (6.4 $\pm$ 0.4) $\times$ 10$^{12}$ cm$^{-2}$, which yields an abundance with respect to molecular H$_2$ of 4.7 $\times$ 10$^{-11}$. Meanwhile, the extremely low dipole moment (about fifteen times lower) of the lower-energy conformer, cis-cis HOCOOH, precludes its detection. We obtain an upper limit ... : Accepted for publication in The Astrophysical Journal ...