A High-Resolution Rotational Analysis of 2‑Chloroethanol (HOCH₂CH₂Cl) and Its First Vibrationally Excited State

An extensive analysis of the high-resolution rotational spectrum (8-26 GHz, 140-700 GHz, 100-600 cm^-1) of the simplest stable chlorohydrin, 2-chloroethanol, is provided by combining high-resolution infrared, microwave, and millimeter-wave spectra. The ground state and first vibrationally excited state of both chlorine isotopologues (HOCH₂CH₂ ³⁵Cl and HOCH₂CH₂ ³⁷Cl) are well treated using a single-state distorted rotor Hamiltonian in the A reduction and I ^r representation, reporting up to a full set of octic distortion constants. The extended microwave spectrum collected and the well-resolved quadrupole splitting observed therein allowed for the further refinement of quadrupole coupling parameters. Inclusion of rotationally resolved infrared transitions enabled the accurate and precise determination of the vibrational band origin of ν₂₁ for HOCH₂CH₂ ³⁵Cl (150.908 599 5 (43) cm^-1). The high spectral density made measurement and least-squares fitting of transitions in both rotational and high-resolution infrared spectra challenging and is the likely source of the larger-than-expected σ_fit value of up to 0.060 MHz for each fit. Nevertheless, the extended millimeter-wave spectrum reported here provides spectral frequencies that directly overlap with astronomical data, allowing for a more thorough search for this species in the interstellar medium. Despite its expected formation from HCl with either oxirane or ethylene glycol in the interstellar medium, 2-chloroethanol continues to evade detection. We report upper limits on the column density toward 30 astrophysically diverse regions. The reported upper limits do not provide significant new constraints on the chemistry of this species in the interstellar medium and highlight the limited knowledge of interstellar chlorine chemistry.