Laboratory measurements and astronomical search for cyanomethanimine⋆
1 Dipartimento di Chimica “Giacomo Ciamician”, Università di Bologna, via F. Selmi 2, 40126 Bologna, Italy
2 INAF, Osservatorio Astronomico di Arcetri, Largo E. Fermi 5, 50125 Firenze, Italy
3 Scuola Normale Superiore, Piazza dei Cavalieri 7, 56126 Pisa, Italy
4 Univ. Grenoble Alpes, CNRS, Institut de Planétologie et d’Astrophysique de Grenoble (IPAG), 38000 Grenoble, France
5 IGN, Observatorio Astronómico Nacional, Calle Alfonso XII, 28004 Madrid, Spain
6 Grupo de Astrofísica Molecular. Instituto de CC. de Materiales de Madrid (ICMM-CSIC). Sor Juana Inés de la Cruz 3, Cantoblanco, 28049 Madrid, Spain
Received: 19 September 2017
Accepted: 16 October 2017
Context. C-cyanomethanimine (HNCHCN), existing in the two Z and E isomeric forms, is a key prebiotic molecule, but, so far, only the E isomer has been detected toward the massive star-forming region Sagittarius B2(N) using transitions in the radio wavelength domain.
Aims. With the aim of detecting HNCHCN in Sun-like-star forming regions, the laboratory investigation of its rotational spectrum has been extended to the millimeter-/submillimeter-wave (mm-/submm-) spectral window in which several unbiased spectral surveys have been already carried out.
Methods. High-resolution laboratory measurements of the rotational spectrum of C-cyanomethanimine were carried out in the 100–420 GHz range using a frequency-modulation absorption spectrometer. We then searched for the C-cyanomethanimine spectral features in the mm-wave range using the high-sensitivity and unbiased spectral surveys obtained with the IRAM 30-m antenna in the ASAI context, the earliest stages of star formation from starless to evolved Class I objects being sampled.
Results. For both the Z and E isomers, the spectroscopic work has led to an improved and extended knowledge of the spectroscopic parameters, thus providing accurate predictions of the rotational signatures up to ~700 GHz. So far, no C-cyanomethanimine emission has been detected toward the ASAI targets, and upper limits of the column density of ~1011–1012 cm-2 could only be derived. Consequently, the C-cyanomethanimine abundances have to be less than a few 10-10 for starless and hot-corinos. A less stringent constraint, ≤10-9, is obtained for shocks sites.
Conclusions. The combination of the upper limits of the abundances of C-cyanomethanimine together with accurate laboratory frequencies up to ~700 GHz poses the basis for future higher sensitivity searches around Sun-like-star forming regions. For compact (typically less than 1″) and chemically enriched sources such as hot-corinos, the use of interferometers as NOEMA and ALMA in their extended configurations are clearly needed.
Key words: ISM: molecules / molecular data / methods: data analysis / methods: laboratory: molecular
The complete list of the measured transitions for Z- and E-C-cyanomethanimine is only available at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (22.214.171.124) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/609/A121
© ESO, 2018