We present the first detection of (Z)-1,2-ethenediol, (CHOH)₂, the enol form of glycolaldehyde, in the interstellar medium toward the G+0.693−0.027 molecular cloud located in the Galactic Center. We have derived a column density of (1.8 ± 0.1) × 10¹³ cm⁻², which translates into a molecular abundance with respect to molecular hydrogen of 1.3 × 10⁻¹⁰. The abundance ratio between glycolaldehyde and (Z)-1,2-ethenediol is ∼5.2. We discuss several viable formation routes through chemical reactions from precursors such as HCO, H₂CO, CHOH, or CH₂CHOH. We also propose that this species might be an important precursor in the formation of glyceraldehyde (HOCH₂CHOHCHO) in the interstellar medium through combination with the hydroxymethylene (CHOH) radical.

The accuracy of rotational parameters obtained from high-level quantum-chemical calculations is discussed for molecules containing second-row atoms. The main focus is on computed rotational constants for which two statistical analyses have been carried out. A first benchmark study concerns sulfur-bearing species and involves 15 molecules (for a total of 74 isotopologues). By comparing 15 different computational approaches, all of them based on the coupled-cluster singles and doubles approach (CCSD) augmented by a perturbative treatment of triple excitations, CCSD(T), we have analyzed the effects on computed rotational constants due to (i) extrapolation to the complete basis-set limit, (ii) correlation of core electrons, and (iii) vibrational corrections to rotational constants. To extend the analysis to other molecules containing second-row elements, as well as to understand the effect of higher excitations, a second benchmark study involving 11 molecules (for a total of 54 isotopologues) has been performed. Finally, the rotational parameters of seven sulfur-containing molecules of astrochemical interest (CCS, C₃S, C₄S, C₅S, HCCS⁺, HC₄S⁺, and HOCS⁺/HSCO⁺) have been computed and compared to experimental data, when available, also addressing the direct comparison of simulated and experimental rotational spectra.