Laboratory detection and astronomical study of interstellar acetohydroxamic acid, a glycine isomer

¹ Grupo de Espectroscopía Molecular (GEM), Edificio Quifima, Área de Química-Física, Laboratorios de Espectroscopía y Bioespectroscopía, Universidad de Valladolid, Parque Científico UVa, Unidad Asociada CSIC, 47011 Valladolid, Spain
e-mail: jlalonso@qf.uva.es
² Centro de Astrobiología, Consejo Superior de Investigaciones Científicas–Instituto Nacional de Tecnica Aeroespacial “Esteban Terradas”, 28850 Madrid, Spain
³ Department of Chemistry, Massachusetts Institute of Technology, Cambridge, MA 02139, USA
⁴ National Radio Astronomy Observatory, Charlottesville, VA 22903, USA

Received: 23 June 2022
Accepted: 18 August 2022

Abstract

Aims. In this work, we aim to achieve the first laboratory detection of acetohydroxamic acid (CH₃CONHOH), a relevant glycine isomer, to enable its eventual identification in the ISM.

Methods. We employed a battery of state-of-the-art rotational spectroscopic techniques in the time domain to measure the microwave spectrum of acetohydroxamic acid. We then used the spectral GOTHAM survey performed with the Green Bank Telescope (GBT) to search for the lowest-energy Z-conformer toward the cold and quiescent molecular cloud TMC-1. We also employed a sensitive spectral survey of the chemically rich Galactic Center molecular cloud G+0.693-0.027, based on IRAM 30 m and Yebes 40 m observations.

Results. We report direct experimental frequencies of the ground state of acetohydroxamic acid (up to 40 GHz). The ¹⁴N nuclear quadrupole hyperfine structure and the A-E splittings due to the internal rotation were observed and analyzed. Hence, a precise set of the rotational spectroscopic parameters were determined for the two distinct conformers, Z- and E-acetohydroxamic acid, which is the initial and prerequisite step of their radio astronomical search in the ISM using low-frequency surveys. We report the nondetection of acetohydroxamic acid toward both astronomical sources. We derive an upper limit to the column density of this molecule very similar to that obtained for glycine. Its corresponding molecular abundance with respect to molecular hydrogen is found to be ≤1 × 10⁻⁹ and 2 × 10⁻¹⁰ in TMC-1 and G+0.693-0.027, respectively, which further constrain the abundance of this glycine isomer in the ISM.