Quantum Chemical Study On The Global Potential Energy Surface Of C₃O₂ Molecule

Carbon suboxide（C₃O₂）has a 150-year-long history of research and has a wide range of applications in different fields.As one of the classical laboratory carbon sources,it enjoys an important position in organic synthetic chemistry.It has important research value in coordination chemistry,atmospheric chemistry,the origin of life,and interstellar chemistry.It is an objective law that chemical research always follows that structure determines properties,and all in-depth studies should be based on accurate structure.However,the determination of the gas-phase structure of the C₃O₂ molecule is always a challenge for experiments.For this reason,in this paper,the gas-phase geometry of C₃O₂ is recalculated using a high-precision calculation method to obtain a sharper CCC bending angle than that of experiments.Secondly,due to the limited research on the isomerization of C₃O₂,this paper conducts a systematic study on the isomerization for the first time and establishes the global reaction potential energy surface of the singlet and triplet states.Finally,based on the establishment of the global potential energy surface,the important reaction model O+C₃O is re-examined in this paper,and a new reaction mechanism is obtained.Detailed research contents are summarized as follows:（1）“Gold standard”study of C₃O₂ molecule:C₃O₂ in gas-phase has still encountered significant debated in the structure and bonding.The key lies in the accurate determination of the CCC angle.In this work,we applied the“gold standard”method,i.e.,CCSD（T）,to revise the rather challengeable CCC angle.To our great surprise,our CCSD（T）/aug-cc-pVnZ（n=T/Q/5）calculations consistently predicted a much more acute CCC angle（ca.148°）than the widely accepted value 156°from experiment and computation.（2）Study on the isomerization and dissociation stability of C₃O₂ molecule:The electronic structure of C₃O₂ and the possibility of interstellar existence have continued to be in hot debate.In addition,it is surprising that other non-chain structure isomers are almost unnoticed.To establish more models of C₃O₂ chemical reaction and explore the possibility of other isomers except for chain-like structure,we have constructed the first extremely comprehensive global potential energy surface containing single and triplet state reaction channels of C₃O₂.At the CBS-QB3 computational level,we obtained 23 new isomers and 62 new transition states.（3）Accurate quantum chemical studies at the CCSD（T）/CBS//CCSD/cc-p VTZ level predicted the depletion of C₃O by both singlet and triplet O-atoms to be barrierless,leading to the astrophysically very abundant CO plus triplet CCO.The barrierless nature of the reaction fully complied with the long conjecture,whereas the product differed significantly.The computational work in this paper provides fundamental but valuable theoretical information for understanding the carbon and oxygen cycles in astrophysics.