Gas Phase Formation Of Organic Nitriles(C5H5N)in The Extraterrestrial Environments

Organic nitriles are important nitrogen reservoirs in interstellar media and also important precursors for biologically relevant molecules.The formation mechanism of pyridine（C₅H₅N）and its isomers has long been studied,but has never been detected in interstellar media.Therefore,there is an urgent need for experimental and theoretical studies on reaction kinetics.This article combines synchrotron vacuum ultraviolet photoionization experiments and quantum chemical calculations to study the reaction mechanism between cyanomethyl radicals（CH₂CN）and propyne/allene（C₃H₄）in high temperature interstellar environments.The main content arranges as follows:First,based on a microfluidic experimental platform,CH₂CN radicals react separately with propyne or allene in a high temperature interstellar environment,and the synchrotron vacuum ultraviolet radiation was scanned within the range of 8.00-10.00 e V to detect all molecules involved in the reaction by single-photon ionization,obtaining photoionization mass spectra and photoionization efficiency（PIE）curves.Then,the adiabatic ionization energies（AIEs）of each C₅H₅N isomer were calculated at the CCSD（T）/CBS//B3LYP/cc-p VTZ level,and the corresponding theoretical PIE curves were calculated using the program ez FCF.The experimental PIE curves were compared with the calculated results and database data,while the structures of all molecules involved in the reaction were quantitatively analyzed.It was found that E-1-cyanobutadiene and Z-1-cyanobutadiene,both with AIEs of 9.65 e V,are the most probable products of the reaction.Second,a double reaction potential energy surface for the reaction of CH₂CN radical with propyne or allene to form C₅H₅N isomers was constructed at the CCSD（T）/CBS//B3LYP/cc-p VTZ level of calculation.The results showed that CH₂CN radical can add to propyne or allene without a barrier,and the main products of the reaction are possibly gauche-E-1-cyano-1,3-butadiene and E-1-cyano-1,3-butadiene.The reaction pathways of two reaction systems have some intersection.Based on this,the rate constants and product branching ratios of each reaction process were further calculated using the Rice-Ramsperger-Kassel-Marcus theory.The results showed that when the internal energy of the molecule is within the range of 115-126 k J·mol^-1,the main reaction product is gauche-E-1-cyano-1,3-butadiene.The yield of E-1-cyano-1,3-butadiene increases with temperature,but its yield does not exceed 1%.Pyridine therefore cannot be generated.This article systematically studies the reaction mechanism of CH₂CN radical with C₃H₄ to generate C₅H₅N isomers in high temperature interstellar environments.The experimental and calculated results can be used to supplement the photoionization cross section database of interstellar molecules,effectively predict the observability of relevant interstellar molecules,and lay a foundation for studying the origin of interstellar molecules by a combination means of optics and physical chemistry.