SIMBAD references

Crossed molecular beam experiments of cyano radicals, CN(X²Σ⁺, ν=0), in their electronic and vibrational ground state reacting with unsaturated hydrocarbons acetylene, C₂H₂(X¹Σ⁺_g), ethylene, C₂H₄(X¹A_g_), methylacetylene, CH₃CCH(X¹A₁), allene, H₂CCCH₂(X¹A₁), dimethylacetylene, CH₃CCCH₃(X¹A₁'), and benzene, C₆H₆ (X¹A_1g_), were performed at relative collision energies between 13.3 and 36.4 kJ.mol^–1 to unravel the formation of unsaturated nitriles in the outflows of late-type AGB carbon stars and molecular clouds. In all reactions, the CN radical was found to attack the π electron density of the hydrocarbon molecule with the radical center located at the carbon atom; the formation of an initial addition complex is a prevalent pathway on all the involved potential energy surfaces. A subsequent carbon-hydrogen bond rupture yields the nitriles cyanoacetylene, HCCCN (X¹Σ⁺), vinylcyanide, C₂H₃CN (X¹A'), 1-methylcyanoacetylene, CH₃CCCN (X¹A₁), cyanoallene, H₂CCCH(CN) (X¹A'), 3-methylcyanoacetylene, HCCCH₂CN(X¹A'), 1,1-cyanomethylallene, H₂CCC(CN)(CH₃) (X¹A'), and cyanobenzene, C₆H₅CN (X¹A₁). In case of acetylene and ethylene, a second reaction channel involves a [1, 2]-H atom shift in the initial HCCHCN and H₂CCH₂CN collision complexes prior to a hydrogen atom release to form cyanoacetylene, HCCCN (X¹Σ⁺), and vinylcyanide, C₂H₃CN (X¹A'). Since all these radical-neutral reactions show no entrance barriers, have exit barriers well below the energy of the reactant molecules, and are exothermic, the explicit identification of this CN versus H atom exchange pathway under single collision conditions makes this reaction class a compelling candidate to synthesize unsaturated nitriles in interstellar environments holding temperatures as low as 10 K. This general concept makes it even feasible to predict the formation of nitriles once the corresponding unsaturated hydrocarbons are identified in the interstellar medium. Here HCCCN, C₂H₃CN, and CH₃CCCN have been already observed; since CH₃CCH is the common precursor to H₂CCCH(CN)/CH₃CCCN and the latter isomer has been assigned unambiguously toward TMC-1 and OMC-1, H₂CCCH(CN) is strongly expected to be present in both clouds as well. The formation of isonitrile isomers was not observed in our experiments. Since all reactions to HCCNC, C₂H₃NC, CH₃CCNC, H₂CCCH(NC), H₂CCC(NC)(CH₃), and C₆H₅NC are either endothermic or the exit barrier is well above the energy of the reactants, neutral-neutral reactions of cyano radicals with closed shell unsaturated hydrocarbons cannot synthesize isonitriles in cold molecular clouds. However, in outflow of carbon stars, the enhanced translational energy of both reactants close to the photosphere of the central star can compensate this endothermicity, and isonitriles might be formed in these hotter environments as well.