氧原子簇O_x^y(x=2～6,y=-2～2)的结构、能学与光谱性质

Geometries, Energetics and Spectroscopic Properties of Oxygen Clusters O_x^y (x=2~6, y=-2~2)

在B3LYP/ 6- 311G(d ,p)水平上 ,对氧原子簇Oxy(x =2～ 6,y =- 2～ 2 )的结构、能学与光谱性质进行了量子化学从头计算 ,对 3O2 和 2 O2 +的基态和激发态进行了CASSCF计算。结果表明 ,氧分子及其离子的体系总能量大小为 3O2 ( 3Σg- ) <2 O2 - ( 2 Πgi) <1O2 ( 1Δg) <1O2 - 2 ( 1Σg+)<2 O2 +( 2 Πg) <1O2 +2 ( 1Σg+)。活性的二重态氧分子负离子2 O2 - ( 2 Πgi)在相对能量上只比三重态的中性氧分子 3O2 ( 3Σg- )高 2 8kJ/mol。对于弯曲型 (Structure -I)的臭氧分子 (O3)及其离子 ,其体系总能量相对次序为 2O3- ( 2 B1) <1O3( 1A1) <3O3( 3B2 ) <1O3- 2 ( 1A1) <2 O3+( 2 A1)。氧四聚体 (O4 )及其离子的体系总能量相对大小为 2O4 - (Cs 弯曲型 ,2A′) <2 O4 - (C2v面心三角型 ,2 A2 ) <2 O4 - (D∞h直线型 ,2Σg) <1O4 (Cs 弯曲型 ,1A′) <1O4 (D∞h直线型 ,1Σg) <1O4 (D4h正方型 ,1A1g) <1O4 (C2v面心三角型 ,1A1) <2 O4 - (D4h正方型 ,1A1g) <2 O4 +(D∞h直线型 ,2Σg) <2 O4 +(Cs 弯曲型 ,1A′)。相对能量最低的氧四聚体物种是呈椅形的带一个负电荷的负离子 2 O4 - (Cs 弯曲型 ,2 A′) ,其特征振动频率应出现在 1179和 134 9cm- 1。共面三角双锥型的 1O5(C2v,1A1)相对能量最低 ,其与A字型

The geometries, energetics and spectroscopic properties of oxygen clusters, O x y (x=2~6, y=-2~2), were investigated at the B3LYP/6-311G (d, p) level. The CASSCF calculations were carried out for the ground and excited states of 3O 2 and 2O 2 +. The total energy is 3O 2( 3Σ g -)< 2O 2 -( 2Π gi )< 1O 2( 1Δ g)< 1O 2 -2 ( 1Σ g +)< 2O 2 +( 2Π g)< 1O 2 +2 ( 1Σ g +). The relative energy of the active doublet anion of oxygen molecule, 2O 2 -( 2Π gi ), is only 28 kJ/mol higher than the triplet neutral oxygen molecule, 3O 2( 3Σ g -). The calculated O-O vibrational frequencies all are in good agreement with the experimental values. They are 1577 (1580), 1139 (1090), 1563 (1484), 627 (615~545) and 1993 (1905) cm -1 , where the O-O vibrational frequency values in parentheses are experimental values, for 3O 2( 3Σ g -), 2O 2 -( 2Π gi ), 1O 2( 1Δ g), 1O 2 -2 ( 1Σ g +) and 2O 2 +( 2Π g), respectively. Moreover, the O-O vibrational frequency of 1O 2 +2 ( 1Σ g +) was computed as 2368 cm -1 which has not been reported before at both experimental and theoretical levels. Both bent and linear geometries of O 3 were studied. The bent-types of O 3 are more favorable than the linear-type in energy. Three types of structure for oxygen trimers are calculated at the B3LYP/6-311G (d, p) level. They are the structure-I with an obtuse angle of O-O-O, the structure-II with an acute angle of O-O-O, and the structure-III of linear type. For a bent-type structure of O 3 species (structure-I), the total enegy is 2O 3 -( 2B 1)< 1O 3( 1A 1)< 3O 3( 3B 2)< 1O 3 -2 ( 1A 1)< 2O 3 +( 2A 1). The optimization of geometry at B3LYP/6-311G (d, p) level indicated that the species of 2O 3 -( 2B 1) with 1.3573 of O-O bond length and 115.6584 o of O-O-O bond anger is the ground state of O 3. The total energy of O 4 species and their ions is 2O 4 -(C s, 2A′, bend-type)< 2O 4 -(C 2v , 2A 2, face-centered triangle-type)< 2O 4 -(D ∞h , 2Σ g, linear-type)< 1O 4(C s, 1A′, bend-type)< 1O 4(D ∞h , 1Σ g, linear-type)< 1O 4(D 4h , 1A 1g , square-type)< 1O 4 (C 2v , 1A 1, face-centered triangle-type)< 2O 4 -(D 4h , 1A 1g , square-type)< 2O 4 +(D ∞h , 2Σ g, linear-type)< 2O 4 +(C s, 1A′, bend-type). The species with the lowest relative energy is an anion, 2O 4 -(C s, 2A′, bend-type), with chair form geometry and characteristic vibronic frequencies of 1179 and 1349 cm -1 . The relative energy of 1O 5 (C 2v , 1A 1) with coplanar-triangle-bicone geometry is the lowest among the O 5 species and their ions, which may be a resonance structure with 1O 5 (C 2v , 1A 1) of A-type. Their characteristic vibronic frequency is 1302 cm -1 . The relative energy of the O 6 species and their ions with hexagon geometry is lower than one with linear geometry. Their infrared vibronic intensity may be weak and unobservable but the Raman vibronic intensity may be strong and observable based on their symmetry.