关键词: 密度泛函, 质子亲合能, 优化几何结构, HFe(CO)⁺₅

Abstract: The geometry configurations of HFe(CO)⁺₅ and Mn(CO)^-₅ are optimized with density functional method at LDA and NL/LDA approximation levels. The proton affinity EPA of Fe(CO)₅ is estimated as 751.6kJ/mol from the results of NL/LDA. The EPA of Fe(CO)₅ is in between those of HCN and NH₃， which gives an explanation to the experimental facts that, on the one hand, Fe(CO)₅ snatches a proton from H₂CN⁺ conveniently, onthe other hand, it is impossible to transfer proton from NH⁺₄ to Fe(CO)₅. There is symmetry transformation of geometry configuration involving in the proton ionization reaction of HFe(CO)⁺₅ ,i.e. from C_4v point group symmetry of Fe(CO)₅ in HFe(CO)⁺₅ to D3h of free Fe(CO)₅, which is similar to the geometry relaxation in proton ionization of isoelectronic HMn(CO)₅. The calculated relaxation energy for the molecular fragment Fe(CO)₅ is -59.78kJ/mol. Our investigation also shows that the backdonated π bonding,Fe→CO，is strengthened after ionization of H⁺ from HFe(CO)⁺₅ ,leading to the shortening of the Fe--C bond length and lengthening of the C--O bond length; synchronously, the electron charge distributed on the Fe atom decreases, while negative charges on the C and O atoms increase. The Mulliken population analysis gives the same tendency, i.e. the F--C bond orders increase and the C--Obond orders decrease after ionization of H⁺ from HFe(CO)⁺₅ .

Key words: density functional theory, proton affinity, geometry optimization, HFe(CO)⁺₅