[H,O,C,N,Mg] Molecule And Ion (Ⅰ) Theoretical Study On The Structure And Stability

Reactions of Mg and Mg⁺with small organic and inorganic molecules not only are important paths to construct Mg-bearing chemical bonds,but also provide eligible target systems for the investigations of the reaction dynamics in forming those Mg-bearing chemical bonds using ground-state and excited Mg and Mg⁺as reactants.Also,this kind of reactions has challenged the theoretical and computational chemistry because the interaction in Mg-bearing bonds may be ionic nature,covalent nature,or a mixture of both,which leads to a strong dependence of the theoretically predicted molecular structures and properties on computational method and level of theory.Moreover,several Mg-including species have been detected in many interstellar regions.The related investigations of their forms,interstellar distribution,abundance,and formation mechanism are of great significance to reveal the composition and evolution of celestial bodies.In this study,we performed a quantum-mechanics computational study of the reactions of Mg and Mg⁺with HNCO and its isomers,which would provide new targets and candidates for laboratory syntheses and astronomical observations.We assessed the dependence of the theoretical molecular geometries and properties on computational method and level of theory for the reactions of Mg with HNCO and its isomers.Based on the constructed reaction potential energy profiles,we determined the thermodynamical and kinetic stabilities of the located minima of the[H,O,C,N,Mg]system.Further,the electronic density difference,natural bond orbital,topology analysis for chemical bonds,Laplacian of electronic density etc.were employed to analyze the bonding nature of Mg-bearing bonds in detail.Moreover,for kinetically and thermodynamically controlled products,we used high-level theoretical methods and computational levels to predict their anharmonic analytical frequencies,as well as some molecular constants,involving equilibrium and vibrationally averaged ground-state electric dipole moments,ground-state and equilibrium rotational constants,centrifugal distortion constants,and vibration-rotation interaction constants.These results provided a support of detailly theoretical data for the laboratory determination and astronomical observation of the main products of the reactions of Mg with HNCO and its isomers.For the reactions of Mg⁺with[H,N,C,O]isomers,we also evaluated the effect of computational method and level on the located minima and gave the believable levels of theory for such a kind of molecules.Based on the geometries and bonding characteristics of the located[H,O,C,N,Mg]⁺isomers,we selected several representative products and analyze their electronic structures,in which the changes in bond length and bond order relative to[H,N,C,O]reactants,as well as charge distribution and bonding nature,were detailly discussed.Furthermore,we theoretically predicted the main products of the complexation reactions of Mg⁺with[H,N,C,O]isomers on the basis of the computed reaction energies.Further,we investigated the photo-induced dissociation channels and the distribution of dissociation fragment products for those main complexation products and predicted the peaks of ion fragments that can be observed in mass spectrum.These results gave a detailed theoretical prediction for the complexation reactions of Mg⁺with HNCO and its isomers and the photo-induced dissociation reactions of the resulting complexation products and provided a strong support of theoretical data for possible experiments in the future.