PdO~(0,±1),PdH~(0,±1)及PdOH分子结构和电子性质的从头计算

利用多种从头计算方法对PdO0,±1,PdH0,±1以及PdOH的结构和电子性质进行了理论研究.优化了PdO分子两个能量相近的态(3Π和3Σ-),结果表明PdO的3Π态较3Σ-态更为稳定,在单双激发耦合簇理论(CCSD)水平下3Σ-态的总能量比3Π态的高出0.286eV.在结构优化的基础上计算了PdO以及PdH的绝热电离能(AIE)和电子亲和能(AEA),计算结果与实验值符合得很好.PdOH的基态为Cs对称性的角型结构Pd—OH(2A′态),另外还优化得到两个2A″态的亚稳结构,分别对应于Pd—OH和O—Pd—H,CCSD水平下两个亚稳态的总能量较基态分别高0.405和2.284eV,优化得到了连接这两个2A″态的过渡态,并计算了相应的反应能垒.     

水蒸汽在Pd表面吸附的热力学

用密度泛函方法和相对论有效原子实势分别对PdOH2、PdOH 及PdO 的几何构型进行了优化, 得到PdOH2分子为Cs构型, Pd 与H2O 分子不在同一平面, RPdO=0.2283 nm; PdOH 分子为2A'态, RPdO=0.1965 nm, ROH=0.0968 nm, ∠PdOH=110.186°; PdO分子基态为3Π, RPdO=0.1858 nm. 根据电子-振动近似理论计算了不同温度下金属Pd与H2O、OH及游离态O原子反应的生成热力学函数, 导出了反应平衡压力随温度的变化关系, 分析认为水蒸汽引起Pd合金膜中毒是由于H2O分子的离解产物OH和O原子吸附在膜表面所致.     

NaC分子基态及其低电子激发态

运用包含Davidson修正的多参考组态相互作用(MRCI+Q)方法结合6-311++G(3df,3pd)基组计算了NaC分子基态(X4∑)以及三个低电子激发态(a2Π, b2∑, A4Π)的势能曲线(PECs), 确定出相应态的平衡键长Re和垂直激发能Te. 然后将PECs拟合到Murrel-Sorbie(MS)解析势能函数形式, 继而获得各态的光谱数据: 谐振频率ωe、离解能De、非谐性常数ωeΧe、转动常数Be、Drot和振转耦合常数αe. 计算结果表明: X4∑、a2Π、b2∑是三个束缚电子态. 基态X4∑的平衡键长为0.2259 nm, 谐振频率为431 cm-1, 离解能为1.92 eV, 目前计算值与实验结果和其它理论值一致. a2Π和b2∑激发态的核间距、谐振频率分别为0.2447、0.2369 nm 和329、335 cm-1, Te分别为1.58 和1.75eV, De则为0.71和0.42 eV. A4Π态为排斥态, 其相对基态的垂直激发能为2.48 eV. 通过求解核运动的薛定谔方程找到了转动量子数J=0时NaC分子三个低电子态(X4∑, a2Π, b2∑)的全部振动能级和转动惯量.     

C2F5I分子C-I键解离的自旋-轨道从头算研究

采用考虑相对论效应的6-311G**全电子基组与多参考微扰理论, 计算了该分子的包含自旋-轨道耦合效应的垂直激发能和基态、激发态C—I键解离势能曲线. 理论计算发现, 势能曲线33A'与11A', 21A'出现交叉, 交叉区域在C—I键长为0.241 nm附近; 基态11A'到激发态33A'(3Q0)的垂直激发能为4.658 eV, 与实验值4.662 eV非常吻合. 讨论了C2F5I分子作为碘激光介质的可行性.     

羰基氧化物RR^1COO的电子结构

本文采用6-31G基组的abinitio方法对羰基氧化物RR^1COO(R,R^1=H,F,CH~3)进行几何构型优化计算,研究其基态的电子结构。结果表明,RR^1COO的稳定结构为双自由基型,其单重态和双重态的相对稳定性受取代基的影响。H~2COO、H(CH~3)COO和(CH~3)~2COO的基态为单重态(^1A),HFCOO和F~2COO的基态为三重态(^3A),HFCOO和H(CH~3)COO的顺式结构比反式稳定。     

羰基氧化物RR^1COO的电子结构

本文采用6-31G基组的ab initio方法对羰基氧化物RR~1COO(R,R~1=H,F,CH_3)进行几何构型优化计算,研究其基态的电子结构.结果表明,RR~1COO的稳定结构为双自由基型,其单重态和双重态的相对稳定性受取代基的影响.H_2COO、H(CH_3)COO和(CH_3)_2COO的基态为单重态(~1A),HFCOO和F_2COO的基态为三重态(~3A),HFCOO和H(CH_3)COO的顺式结构比反式稳定.     

SiNP分子结构及稳定性的理论研究

采用B3LYP/6-311G(d),QCISD和CCSD(T)方法,对单重态和三重态SiNP体系的异构化进行了研究.在QCISD/6-311G(d)水平下,得到了7个稳定的异构体,它们由4个过渡态所连接,其中三重态线型异构体SiNP(31,3Σ1),单重态环状异构体SiNP(14,1A')和单重态线型异构体SiNP(11,1Σ)都具有较大的热力学及动力学稳定性.     

PdH2、YH2分子的结构与势能函数

用密度泛函理论的B3LYP方法,对钯和钇原子采用SDD收缩价基函数,氢原子采用6-311＋＋G**全电子基函数,对PdH2和YH2体系的结构进行优化计算,得到PdH2分子最稳态为C2v构型,电子组态为1A1,平衡核间距RPdH=0.1692 nm,键角∠HPdH=29.4°,离解能De=5.5212 eV,基态简正振动频率:ν1(b2)=1470.1 cm－1、ν2(a1)=1007.9 cm－1、ν3(a1)=2907.0 cm－1.YH2分子最稳态也为C2v构型,电子组态2A1,RYH=0.1962 nm,∠HYH=114.3°,De=5.6691 eV,基态简正振动频率:ν1(b2)=1457.9 cm－1、ν2(a1)=476.0 cm－1、ν3(a1)=1506.3 cm－1.由微观过程的可逆性原理分析了分子的可能离解极限.并用多体项展式理论方法分别导出基态PdH2和YH2分子的势能函数,其等值势能面图准确地再现了PdH2和YH2分子的结构特征和离解能,由此讨论了Pd ＋ H2和Y ＋ H2分子反应的势能面静态特征.     

AlnO2±团簇结构的几何特征与稳定性

采用密度泛函理论(DFT)的B3LYP方法,在6-311G**水平上对AlnO2±(n=1-10)团簇的几何和电子结构进行了理论计算.讨论了混合团簇的基态结构与振动频率,以及电荷转移与分子轨道.结果表明,AlnO2±(n>1)团簇的基态结构都是2个较小的AlmO(m相似文献   

α-SrMnO3电子结构的第一性原理研究

采用平面波赝势方法对钙钛矿型锰酸盐氧化合物α-SrMnO3的电子结构进行了第一性原理研究. 六方钙钛矿型结构α-SrMnO3化合物为磁性绝缘体, 磁基态对应于共面八面体及共顶点八面体间的磁性交换作用均为反铁磁性(AFM), 其禁带宽度为1.6 eV; 费米能级附近的Mn3d态与O2p态存在很强的杂化作用, 属于共价绝缘体, 这种强共价性使得Mn4+的自旋磁矩偏离理想值. 采用Noodleman的对称性破缺方法, 根据α-SrMnO3不同磁有序态的总能量拟合出α-SrMnO3中的自旋交换耦合常数. α-SrMnO3的局部微结构(Mn—O—Mn)决定了整个体系的特殊磁性交换作用. 共面及共顶点的八面体间均存在AFM交换作用, 并且共顶点八面体间的AFM作用比较强.     

多组态二级微扰理论计算CH3O2激发光谱以及CH3O2→CH3＋O2解离反应

在C_s对称性和aug-cc-pVTZ基组水平下, 采用全活化空间自洽场方法(CASSCF)研究了CH₃O₂自由基基态及其阴阳离子的12个低激发态. 为了进一步考虑动态电子相关效应, 采用二级多组态微扰理论(CASPT2)获得更加精确的能量值. 所有计算得到的电子态都是价电子态, 而且所得绝热激发能和电子亲和势与实验值非常接近.在CASPT2//CASSCF理论水平下计算了CH₃O₂从²A"和²A'电子态的CH₃O₂→CH₃＋O₂的解离反应的势能曲线(PECs). 优化得到的裂解产物的几何结构和能量与分别优化CH₃和O₂得到的结果进行比较, 从而确定裂解产物的电子态. 结果表明, 从²A"和²A'电子态的解离反应分别对应产物CH₃(²A")＋O₂(³A")和CH₃(²A")＋O₂(¹A").     

N_2O分子C~1Π态的吸收光谱及解离动力学

通过四波混频差频的方法产生高分辨的真空紫外激光,用以测量143.6至146.9 nm范围内的射流冷却N2O分子吸收光谱,对应于C1Π←X1Σ+的吸收跃迁.谱图显示出三个分立的振动谱峰叠加在宽吸收背景上,谱峰间隔分别是521和482 cm-1.前人的高精度量子化学计算表明C1Π态在N—O键长方向表现为无势垒的排斥态,而在N—N键伸缩及N2O弯曲振动方向则表现为束缚态,因此观测到的振动谱峰被归属为激发态的Feshbach共振.通过反Fourier变换可以得到Feshbach共振对应的非稳定周期轨道的特征周期为61 fs,相应的振动频率为546 cm-1.鉴于这一频率与弯曲振动频率非常接近,非稳定周期轨道被认为是由C1Π态的弯曲振动与解离运动相互作用而形成的,N—N伸缩振动没有参与形成非稳定周期轨道.由此,N2O分子C1Π态光激发-解离过程得以清晰地阐述.     

MRD CI study of the photodissociation of HO2 into OH(X2II) + O(3P, 1D)

A MRD CI procedure has been used to calculate several electronic states of the hydroperoxyl radical. The basis set is of double-zeta plus polarization quality augmented with s- and p-type bond and Rydberg functions. The vertical excitation energies of the lowest eight doublet and six quartet states are reported. Oscillator strengths for transitions form the ground to upper doublet states were calculated. A cut of the potential energy surfaces along the OOH fragmentation pathway is used to discuss the mechanisms of HO₂ photodissociation below 6.4 eV. Arguments are presented which indicate O(¹D) rather than O(³P) is the primary dissociation product, and so support the experimental findings rather than theory in the conflict raised earlier on this matter. Ostensibly the dissociation proceeds diabatically on the surface of the initially populated ²A″(1a″ → 2a″) state yielding OH(X²II) + O(¹D).     

Communication: Multi-state analysis of the OCS ultraviolet absorption including vibrational structure

The first absorption band of OCS (carbonyl sulfide) is analyzed using potential energy surfaces and transition dipole moment functions of the lowest four singlet and the lowest four triplet states. Excitation of the 2 (1)A' state is predominant except at very low photon energies. It is shown that the vibrational structures in the center of the band are due to excitation of the 2 (3)A' triplet state, whereas the structures at very low energies are caused by bending excitation in the potential wells of states 2 (1)A' and 1 (1)A'.     

Surface structure for Au on (0 0 1) SrTiO3

First-principle calculations are performed to study the crystal structure, formation energies, and electronic structures of (0 0 1) SrTiO₃ surfaces with/without Au covered. The initiative Au additive layer is crystallized in a fcc structure with (0 0 1) face on SrO-terminated surface. The bimodal growth trend of Au on TiO₂-terminated surface is qualitatively consistent with the experimental observations. The defect structure of Au occupying the oxygen (O) vacancies of TiO₂-terminated surface is energetically favorable under oxygen-poor conditions, and a feature corresponding to gap states appear and the occupied Ti 3d states disappear.     

Collision energy dependence of the O(1D) + HCl --> OH + Cl(2P) reaction studied by crossed beam scattering and quasiclassical trajectory calculations on ab initio potential energy surfaces

The dynamics of the O(1D) + HCl --> OH + Cl(2P) reaction are investigated by a crossed molecular beam ion-imaging method and quasiclassical trajectory calculations on the three ab initio potential energy surfaces, the ground 1(1)A' and two excited (1(1)A' and 2(1)A') states. The scattering experiment was carried out at collision energies of 4.2, 4.5, and 6.4 kcal/mol. The observed doubly differential cross sections (DCSs) for the Cl(2P) product exhibit almost no collision energy dependence over this inspected energy range. The nearly forward-backward symmetric DCS indicates that the reaction proceeds predominantly on the ground-state potential energy surface at these energies. Variation of the forward-backward asymmetry with collision energy is interpreted using an osculating complex model. Although the potential energy surfaces obtained by CASSCF-MRCI ab initio calculations exhibit relatively low potential barriers of 1.6 and 6.5 kcal/mol for 1(1)A' and 2(1)A', respectively, the dynamics calculations indicate that contributions of these excited states are small at the collision energies lower than 15.0 kcal/mol. Theoretical DCSs calculated for the ground-state reaction pathway agree well with the observed ones. These experimental and theoretical results suggest that the titled reaction at collision energies less than 6.5 kcal/mol is predominantly via the ground electronic state.     

Structures of 1,2,3-trihydroxybenzene in the S0 and S1 states

In this paper we report on the structure and vibrations of gaseous pyrogallol (1,2,3-trihydroxybenzene) in the electronic ground state (S₀) and its first electronically excited state (S₁). Both ab initio CASSCF/CASMP2 calculations as well as R2PI spectroscopy have been performed. From the ab initio calculations three minimum energy structures are obtained and the vibrations of two structures are observed in the R2PI spectra. The minimum energy structures differ by their OH torsional angles. The full three-dimensional potential energy surface of the coupled torsional motions is investigated and the three-dimensional eigenvalues are calculated. The most stable structure of pyrogallol contains two intramolecular hydrogen bonds and turns out to be planar in the S₀ state. In the S₁ state the free OH group is rotated out of the plane of the aromatic ring by about 40°. The strong change in geometry of this structure is predicted by the CASSCF calculations and confirmed by the R2PI spectra of pyrogallol and its deuterated species. The low frequency region of the R2PI spectra can be explained by a torsional motion and the out of plane vibration 17b.     

Additivity of electron correlation energy and the ab initio MO calculation of (0–0) S1←S0 transition energies: polychlorinated dibenzofurans

The energies of the S₀ and S₁ states of polychlorinated dibenzofurans (PCDFs) were calculated using the Hartree–Fock (HF) and configuration interaction-singles (CIS) methods. We can obtain the (0–0) transition energies of PCDFs with good accuracy if the energies calculated using the HF and CIS methods are adjusted to take the electron correlation energy into account. The correlation energy of the S₀ state was calculated using the Møller–Plesset correlation correction truncated at the second order (MP2), and that of the S₁ state was determined using experimental data. The correlation energies for both S₀ and S₁ states were expressed as the sum of the contributions arising from dibenzofuran (DF) and substituted chlorine atoms. The energy of the ground state calculated using the additivity approximation was in good agreement with the energy given directly by the MP2 method. The (0–0) S₁←S₀ transition energies corrected for electron correlation energy agreed well with the available experimental data. The approach proposed in this paper may be useful for the estimation of the electronic transition energy for large aromatic molecules.