Micro- and millimeter-wave spectra of five conformers of cysteamine and their interstellar search

Context. Cysteamine (NH2CH2CH2SH), a molecule of potential astrobiological interest, has not yet been detected in the interstellar medium. Furthermore, the sulfur- stituted isomer of ethanolamine (or 2-aminoethanol) has been recently detected in the molecular cloud G+0.693-0.027. Aims. In order to conduct a new interstellar search for cysteamine in the molecular cloud G+0.693-0.027, its pure rotational spectrum needs to be investigated in the laboratory. Methods. A pulsed-jet Fourier transform microwave spectrometer and a Stark-modulated free-jet millimeter-wave absorption spectrometer were used to measure the purely rotational spectrum of cysteamine in the range of 6.5-18 GHz (46.12-16.66 mm) and 59.6-120.0 GHz (5.03-2.72 mm), respectively. We used a deep spectral line survey toward the molecular cloud G+0.693-0.027 obtained with the IRAM 30 m and Yebes 40 m radiotelescopes to search for cysteamine. Results. We assigned 815 rotational transition lines of five conformers (gGt, gGg, g ' Gg, g ' Gg ', and g'Gt) to fit the rotational constants, quartic centrifugal distortion constants, and the N-14 nuclear quadrupole coupling constants. For four conformers (gGt, gGg, g ' Gg, and g ' Gg '), the S-34 isotopologs were observed, and for two of them (gGg and g'Gg), the C-13 and N-15 isotopolog spectra were also detected; all in natural abundance. The five conformers of cysteamine were not detected toward the G+0.693-0.027 molecular cloud. We derived upper limits for their molecular abundances compared to molecular hydrogen of <(0.2-1.3) x 10(-10). The relative abundances with respect to the oxygen counterpart ethanolamine, previously detected toward this cloud, are NH2CH2CH2OH/NH2CH2CH2SH > 0.8-5.3.