Unearthing the Hidden Interstellar Carbonic Acid (HOCOOH) - A Spectacular Space Discovery!

 Delving into the cosmos after a span of twenty-five years since the identification of the last interstellar carboxylic acid, acetic acid (CH3COOH), the scientific community has unveiled the existence of a new interstellar molecule - the cis-trans form of carbonic acid (HOCOOH). This discovery was made in the Galactic Center molecular cloud G+0.693-0.027, marking HOCOOH as an unprecedented interstellar molecule that comprises three oxygen atoms, and solidifying its position as the third carboxylic acid discovered in the interstellar medium. 

Despite the restrictions of laboratory measurements (up to 65 GHz), the identification of several pairs of unblended lines directly from the astronomical data (between 75-120 GHz) was made possible, resulting in a refined set of spectroscopic constants. The calculated column density for cis-trans HOCOOH amounted to N = (6.4 ± 0.4) × 1012 cm−2, leading to an abundance relative to molecular H2 of 4.7 × 10−11. 

On the other hand, the cis-cis HOCOOH, with its incredibly low dipole moment, remains elusive to detection. An upper limit to its abundance with respect to H2 is determined to be ≤ 1.2 ×10−9, suggesting that cis-cis HOCOOH could be quite abundant in interstellar space, yet nearly undetectable by radio astronomical observations.

The derived cis-cis/cis-trans ratio of ≤ 25 coincides with the smaller energy difference between both conformers compared to the relative stability of trans- and cis-formic acid (HCOOH). Finally, a comparison of these acids in various astronomical environments reinforces the possible link between the chemical content in the interstellar medium and the chemical composition of minor celestial bodies in the Solar System, likely inherited during the star formation process. 

Source: arXiv

Image Credit: NASA/JPL-Caltech - The Galactic Center as visualized in infrared light by NASA’s Spitzer Space Telescope.