Single-Photon Ionization Induced New Covalent Bond Formation in Acrylonitrile(AN)–Pyrrole(Py) Clusters

Abstract

The formation of nitrogen-containing organic compounds is crucial for understanding chemical evolution and the origin of life in the interstellar medium (ISM). In this study, we explore whether acrylonitrile (AN) and pyrrole (Py) can form new nitrogen-containing compounds after single-photon ionization in their gaseous clusters by vacuum ultraviolet (VUV)-infrared (IR) spectroscopy and theoretical calculations. The results show that a strong linear H-bond is formed in neutral AN-Py, while cyclic or bicyclic H-bonded networks are formed in the neutral AN-Py 2 cluster. It is found that the structure containing a new C−C covalent bond between two moieties in (AN-Py) + is formed besides the formation of H-bonded structures after AN-Py is ionized by VUV light. In (AN-Py 2 ) + cluster cations, new C−C or C−N covalent bonds tend to be formed between two Py, with (Py) 2 + as the core in the cluster. The results reveal that new covalent bonds are more likely to be formed between two Py species when AN and Py are present in the cationic clusters. These results provide spectroscopic evidence of the formation of new nitrogen-containing organic compounds from AN and Py induced by VUV, which are helpful for our understanding of the formation of diverse prebiotic molecules in interstellar space.

Internal Energy Dependence of the Pyrrole Dimer Cation Structures Formed in a Supersonic Plasma Expansion: Charge-Resonance and Hydrogen-Bonded Isomers

“…For the example of VUV-generated Py 2 + , the suggested chemically bonded cc1 and cn1 isomers do not convincingly explain the broad and intense transition centered at 3020 cm –1 in the IRPD depletion spectrum, in particular, its blue tail ranging up to 3300 cm –1 . A similar broad and intense band at 3150 cm –1 with blue tail ranges up to 3500 cm –1 was observed in the IR spectrum of VUV-generated (acrylonitrile-Py 2 ) + and explained by an NH···N H-bonded ν NH . In addition, according to the computed potential energy surface diagram, these ion–molecule reactions require at least 2.0 eV activation energy to be initiated from Py 2 + (a) via barriers in collision-free conditions.…”

“…A similar broad and intense band at 3150 cm –1 with blue tail ranges up to 3500 cm –1 was observed in the IR spectrum of VUV-generated (acrylonitrile-Py 2 ) + and explained by an NH···N H-bonded ν NH . 46 In addition, according to the computed potential energy surface diagram, 43 these ion–molecule reactions require at least 2.0 eV activation energy to be initiated from Py 2 + (a) via barriers in collision-free conditions. This energy is much higher than the dissociation energy of Py 2 + (a) of around 1.1 eV, and thus, it is rather unclear how these cc1/cn1 isomers can be stabilized under collision-free conditions.…”