Spectroscopic evidence of the C-N covalent bond formed between two interstellar molecules (ISM): acrylonitrile and ammonia

Acrylonitrile (AN) and ammonia (NH₃) are two important nitrogen-containing interstellar molecules in outer space, especially on Titan. Herein, we measured infrared (IR) spectra of neutral and cationic AN-NH₃complexes by VUV single-photon ionization combined with time-of-flight mass spectrometry. On combining IR spectra with the theoretical calculations, we found that the molecules prefer to form a single-ring cyclic H-bonded structure in the neutral AN-NH₃and (AN)₂-NH₃clusters. However, after ionization of AN-NH₃and (AN)₂-NH₃clusters, a new C-N-covalent bond is confirmed to form directly between AN and NH₃, without any energy barrier in the cationic complexes. Moreover, in the ionized (AN)₂-NH₃cluster, the covalent C-N bond prefers to form between AN and NH₃rather than the two AN groups. These results provide spectroscopic evidence of AN forming a new molecule with NH₃, induced by VUV radiation. The formation of the new C-N bond broadens our knowledge on the evolution of the prebiotic nitrogen-containing molecules in space.