Millimeter-wave spectroscopy and modeling of 1,2-butanediol^⋆

Laboratory spectrum in the 59.6–103.6 GHz region and comparison with the ALMA archived observations

¹ Dipartimento di Chimica “Giacomo Ciamician”, Università di Bologna, Via Selmi 2, 40126 Bologna, Italy
e-mail: assimo.maris@unibo.it
² Dpto. Química Física, Facultad de Ciencia y Tecnología, Universidad del País Vasco (UPV/EHU), Apartado 644, 48080 Bilbao, Spain
³ Basque Centre for Biophysics (CSIC, UPV/EHU), Bilbao, Spain
⁴ Istituto di Radioastronomia (IRA-INAF), Via Gobetti 101, 40129 Bologna, Italy

Received: 24 May 2018
Accepted: 26 July 2018

Abstract

Context. The continuously enhanced sensitivity of radioastronomical observations allows the detection of increasingly complex organic molecules. These systems often exist in a large number of isomers leading to very congested spectra.

Aims. We explore the conformational space of 1,2-butanediol and provide sets of spectroscopic parameters to facilitate searches for this molecule at millimeter wavelengths.

Methods. We recorded the rotational spectrum of 1,2-butanediol in the 59.6–103.6 GHz frequency region (5.03–2.89 mm) using a free-jet millimeter-wave absorption spectrometer, and we analyzed the properties of 24 isomers with quantum chemical calculations. Selected measured transition lines were then searched on publicly available ALMA Band 3 data on IRAS 16293-2422 B.

Results. We assigned the spectra of six conformers, namely aG′Ag, gG′Aa, g′G′Ag, aG′G′g, aG′Gg, and g′GAa, to yield the rotational constants and centrifugal distortion constants up to the fourth or sixth order. The most intense signal belong to the aG′Ag species, that is the global minimum. Search for the corresponding 30_x,30 − 29_x,29 transition lines toward IRAS 16293-2422 B was unsuccessful.

Conclusions. Our present data will be helpful for identifying 1,2-butanediol at millimeter wavelengths with radio telescope arrays. Among all possible conformers, first searches should be focused on the aG′Ag conformers in the 400–800 GHz frequency spectral range.