He-N2O的从头算势能面及振转能级

采用超分子MP4方法和较大的基组计算得到了He-N₂O体系的分子间势能面,发现该势能面有3个极小值点,分别对应T形构型及两个线性He-ONN和He-NNO构型.同时采用离散变量表象方法预测了体系的振转能级,计算结果表明,MP4势能面支持5个振动束缚态.     

He-N2O偶极矩面及振转跃迁强度的理论研究

用超分子MP4方法和大基组(aug-cc-pVTZ)及键函数得到He-N₂O体系的分子间从头算势能面及偶极矩面,用离散变量表象方法计算了⁴He-N₂O及³He-N₂O体系的振转能级,并进一步计算得到其振转跃迁强度,计算结果很好地解释了实验现象.     

Theoretical study of potential energy surface and vibrational spectra of ArF2 system

An ab initio potential energy surface (PES) of ArF2 system has been obtained by using MP4 calculation with a large basis set including bond functions. There are two local minimums on the PES: one is T-shaped and the other is L-shaped. The L-shaped minimum is the global minimum with a well depth of -119.62 cm- 1 at R = 0.3883nm. The T-shaped minimum has a well depth of -85.93cm -1 at R = 0.3486 nm. A saddle point is found at R = 0.3486 and θ = 61° with the well depth of -61.53 cm-1. The vibrational energy levels have been calculated by using VSCF-CI method. The results show that this PES supports 27 vibrational bound states, and the ground states are two degenerate states assigned to the L-type vibration.     

Global ab initio potential energy surfaces for both the ground (X̃1A') and excited (Ã1A') electronic states of HNO and vibrational states of the Renner-Teller Ã1A'-X̃1A' system

The global potential energy surfaces for both the ground (X?(1)A(')) and excited (A?(1)A(')) electronic states of the HNO molecule have been constructed by three-dimensional cubic spline interpolation of more than 17,000 ab initio points, which have been calculated at the internal contracted multi-reference configuration interaction level with the Davidson correction using an augmented correlation-consistent polarized valence quadruple zeta basis set. The low-lying vibrational energy levels for the two electronic states of HNO have also been calculated on our potential energy surfaces including the diagonal Renner-Teller terms. The calculated results have shown a good agreement with the experimental vibrational frequencies of HNO and its isotopomers.     

Electronic structure and bonding in heteronuclear dimers of V, Cr, Mo, and W: a CASSCF/CASPT2 study

Heteronuclear dimers like CrMo, CrW, MoW, VCr, VMo, VW, and their anions have been investigated by means of multiconfigurational quantum chemistry methods, using the complete active space self-consistent field followed by second-order perturbation theory, CASSCF/CASPT2. We explored in great detail several spectroscopic properties such as bond length, potential energy surfaces, dissociation energies, ionization potentials, electron affinities, low-lying excited states, vibrational frequencies, and dipole moments. All proposed dimers show ground states with a pronounced multireference character. The group VI heterodimers have a (1)Σ(+) ground state, while the mixed group V-group VI heterodimers show a (2)Δ ground state. Among all dimers, only VCr presents a potential energy profile with a deep minimum in the d-d region and a shelf-like potential in the s-s region. All the remaining dimers show only the short-range minimum. The largest effective bond order is obtained for the MoW, with a value of 5.2, that is, a weak sextuple bond. Most of the obtained results are valuable tools to drive future experimental investigations.     

SO2基态势能面和振转能级的理论研究

在键长-键角坐标下,精确求解SO₂的核振动方程,并通过与实验数据比较来优化势能参数,由所得势能面计算得到38个振动能级,与实验值相比,均方根误差为0.93cm^-1.计算了³⁴SO₂的部分振动能级以及³²SO₂的J=6以下的部分振动能级,所得结果均与实验值较为吻合     

Ab initio energies and tunneling lifetimes of the doubly charged AH2+ (A = Mg—Ar) diatomics

Potential energy curves for the ground and low-lying excited states of the AH²⁺ (A = Mg—Ar) dications have been calculated using high-level ab initio methods with large atomic orbital basis sets. Quasi-bound potential energy curves with local minima and deprotonation barriers have been found for most of the dications studied. The energies, tunneling lifetimes, and widths of the quasi-bound states have been calculated by numerical solution of the radial Schrodinger equation using the Numeov method. All these dications except ArH²⁺ have low-lying states which support quasi-bound vibrational states. The ArH²⁺ dication has a ²∏_i potential energy curve with a minimum so shallow that it does not support any quasi-bound vibrational states. Results of our calculations are compared with previous ab initio calculations and available experimental data. © 1995 John Wiley & Sons, Inc.     

Ab initio calculations on low-lying electronic states of TeO2 and Franck-Condon simulation of the (1)1B2 <-- X1A1 TeO2 absorption spectrum including anharmonicity

Ab initio calculations have been carried out on low-lying singlet and triplet states of TeO2 at different levels of theory with basis sets of up to the augmented-polarized valence-quintuple-zeta quality. Equilibrium geometrical parameters, harmonic vibrational frequencies, and relative electronic energies of the X1A1, 1B1, 1B2, 1A2, 3A1, 3B1, 3B2, and 3A2 states of TeO2 have been calculated. Potential energy functions (PEFs) of the X1A1 and the (1)1B2 states were computed at the complete-active-space self-consistent-field multireference configuration interaction level, with a basis set of augmented-polarized valence-quadruple-zeta quality. Franck-Condon factors (FCFs) for the electronic transition between the X1A1 and (1)1B2 states of TeO2 were calculated with the above-mentioned ab initio PEFs. The (1)1B2 <-- X1A1 absorption spectrum of TeO2 was simulated employing the computed FCFs, which include Duschinsky rotation and anharmonicity, and compared with the recently published laser-induced fluorescence (LIF) spectrum of Hullah and Brown [J. Mol. Spectrosc. 200, 261 (2000)]. The ab initio results and spectral simulation reported here confirm the upper electronic state involved in the LIF spectrum to be the (1)1B2 state of TeO2 and also confirm the vibrational assignments of Hullah and Brown. However, our simulated spectrum suggests that the reported LIF spectrum from 345 to 406 nm represents only a portion of the full (1)1B2 <-- X1A1 absorption spectrum of TeO2, which extends from ca. 406 to 300 nm. Another dye other than the two used by Hullah and Brown is required to cover the 345-300 nm region of the LIF band. Ab initio calculations show strong configuration mixing of the (1)1B2 electronic surface with higher 1B2 states in a region of large TeO bond length (> or = 2.0 A) and OTeO bond angle (> or = 135.0 degrees).     

Computational analyses of singlet-singlet and singlet-triplet transitions in mononuclear gold-capped carbon-rich conjugated complexes

Density functional theory and CASSCF calculations have been used to determine equilibrium geometries and vibrational frequencies of metal-capped one-dimensional pi-conjugated complexes (H3P)Au(C[triple chemical bond]C)(n)(Ph) (n = 1-6), (H3P)Au(C[triple chemical bond]CC6H4)(C[triple chemical bond]CPh), and H3P--Au(C[triple chemical bond]CC6H4)C[triple chemical bond]CAu--PH3 in their ground states and selected low-lying pi(pi)* excited states. Vertical excitation energies for spin-allowed singlet-singlet and spin-forbidden singlet-triplet transitions determined by the time-dependent density functional theory show good agreement with available experimental observations. Calculations indicate that the lowest energy 3(pi(pi)*) excited state is unlikely populated by the direct electronic excitation, while the low-lying singlet and triplet states, slightly higher in energy than the lowest triplet state, are easily accessible by the excitation light used in experiments. A series of radiationless transitions among related excited states yield the lowest 3(pi(pi)*) state, which has enough long lifetimes to exhibit its photochemical reactivities.     

An ab initio study of the lowest electronic states of yttrium dicarbide, YC2

The low-lying electronic states of yttrium dicarbide have been calculated using highly correlated wave functions and systematic sequences of correlation consistent basis sets. For the (2)A(1) ground electronic state, the near-equilibrium potential energy surface (PES) has been calculated using the coupled cluster method in conjunction with basis sets ranging in size from double to quintuple zeta. The relativistic effects have been taken into account by using pseudopotentials for the Y atom. After extrapolation to the complete basis set limit, additional corrections due to core-valence correlation and spin-orbit effects have also been included. The same approach has been followed for the (2)B(1), (2)B(2), and (2)A(2) states but only the C(2V) PESs have been considered in these cases. For the two (2)A(1) electronic excited states and, for comparison purposes, for the ground state, the multireference configuration interaction (MRCI) approach has been used in conjunction with double-zeta and triple-zeta basis sets for the construction of the PES. The molecular and spectroscopic properties predicted for the ground and excited states investigated in this work compare well with the available experimental data, particularly for the ground electronic state. The 0 K dissociation enthalpy of YC(2), DeltaH(Y-C2)(0 K), and its atomization enthalpy, SigmaD(0), are predicted to be 148.4 and 291.5 kcal/mol, respectively.     

He2+和He2++分子离子基态和激发态的特性研究

采用SAC/SAC-CI方法在CC-PV5Z基组下, 计算研究了He2+、He2++的基态及低激发态的分子特性, 给出了其基态和一些激发态的势能函数和光谱数据(Be、αe、ωe和ωeχe). 从群论出发推导了相应状态的离解极限；与已有实验结果的He2+(X2Σu+)相比, 计算结果令人满意. 还计算了激发态2Πu、4Σu+和4Πg的结构与光谱数据. 对于He2++, 计算的九个电子态中只有三个态(X1Σg+、1Σg+和1Σu+)属束缚态, 并得到了其光谱常数. 用价键理论模型的不相交规则对He2++基态的势能曲线极大点产生的原因做了较好的分析.     

Theoretical study of potential energy surface and vibrational spectra of ArF2 system

Anab initio potential energy surface (PES) of ArF₂ system has been obtained by using MP4 calculation with a large basis set including bond functions. There are two local minimums on the PES: one is T-shaped and the other is L-shaped. The L-shaped minimum is the global minimum with a well depth of -119.62 cm^-1 atR = 0.3883nm. The T-shaped minimum has a well depth of -85.93cm^-1 atR = 0.3486 nm. A saddle point is found atR = 0.3486 and τ = 61° with the well depth of -61.53 cm^-1. The vibrational energy levels have been calculated by using VSCF-CI method. The results show that this PES supports 27 vibrational bound states, and the ground states are two degenerate states assigned to the L-type vibration.     

Quantum chemical investigation of the electronic spectra of the keto, enol, and keto-imine tautomers of cytosine

The low-lying excited singlet states of the keto, enol, and keto-imine tautomers of cytosine have been investigated employing a combined density functional/multireference configuration interaction (DFT/MRCI) method. Unconstrained geometry optimizations have yielded out-of-plain distorted structures of the pi --> pi and n --> pi excited states of all cytosine forms. For the keto tautomer, the DFT/MRCI adiabatic excitation energy of the pi --> pi state (4.06 eV including zero-point vibrational energy corrections) supports the resonant two-photon ionization (R2PI) spectrum (Nir et al. Phys. Chem. Chem. Phys. 2002, 5, 4780). On its S1 potential energy surface, a conical intersection between the 1pipi state and the electronic ground state has been identified. The barrier height of the reaction along a constrained minimum energy path amounts to merely 0.2 eV above the origin and explains the break-off of the R2PI spectrum. The 1pipi minimum of the enol tautomer is found at considerably higher excitation energies (4.50 eV). Because of significant geometry shifts with respect to the ground state, long vibrational progressions are expected, in accord with experimental observations. For the keto-imine tautomer, a crossing of the 1pipi potential energy surface with the ground-state surface has been found, too. Its n --> pi minimum (3.27 eV) is located well below the conical intersection between the pi --> pi and S0 states, but it will be difficult to observe because of its small transition moment. The identified conical intersections of the pi --> pi excited states of the keto cytosine tautomers are made responsible for the ultrafast decay to the electronic ground states and thus may explain their subpicoseconds lifetimes.     

Si2分子基态和低激发态的电子结构

本文用abinitioSOCI／MCSCF／／HF／DH＋d方法计算得到了Si2分子的基态和八个激发态的平衡几何构型、总能量、谐振动频率、零点能以及各个态的势能曲线．讨论了各态键长随电子组态的变化关系，指出了成健轨道中。电子数的增加，是引起键长及谐振动频率变化的重要因素·其中3Πg，5∑；3△u，3∑，未见有关文献报导由于硅藻合物的重要应用价值，人们已对其进行了一些实验和理论研究h，’」．以前的研究主要是讨论其成键性质．由于St。分子结构的特殊性，要想全面了解其成键性质，不仅要研究其基态的电子结构，而且还要研究其激发态的电…     

Excited states of thiophene: ring opening as deactivation mechanism

(Time-dependent) Kohn-Sham density functional theory and a combined density functional/multi-reference configuration interaction method (DFT/MRCI) were employed to explore the ground and low-lying electronically excited states of thiophene. Spin-orbit coupling was taken into account using an efficient, nonempirical mean-field Hamiltonian. Phosphorescence lifetimes were calculated by means of spock.ci, a selecting direct multi-reference spin-orbit configuration interaction program. Throughout this paper, we use the following nomenclature: S1, S2,..., T1, T2,..., denominate electronic structures in their energetic order at the ground state minimum geometry, whereas S1, S2,..., T1, T2,..., refers to the actual order of electronic states at a given nuclear geometry. Multiple minima were found on the first excited singlet (S1) potential energy hypersurface with electronic structures S1 (piHOMO-1-->pi+piHOMO-->pi), S2 (piHOMO-->pi), and S3 (piHOMO-->sigma*) corresponding to the 2 1A1 (S1), 1 1B2 (S2), and 1 1B1 (S3) states in the vertical absorption spectrum, respectively. The S1 and S2 minimum geometries show out-of-plane deformations of the ring. The S3 electronic structure yields the global minimum on the S1 surface with an adiabatic excitation energy of merely 3.81 eV. It exhibits an asymmetric planar nuclear arrangement with one significantly elongated C-S bond. A constrained minimum energy path calculation connecting the S1 and S3 minima suggests that even low-lying vibrational levels of the S1 potential well can access the global minimum of the S1 surface. Nonradiative decay of the electronically excited singlet population to the electronic ground state via a close-by conical intersection will be fast. According to our work, this ring opening mechanism is most likely responsible for the lack of fluorescence in thiophene and the ultrafast decay of the S1 vibrational levels, as observed in time-resolved pump-probe femtosecond multiphoton ionization experiments. An alternative relaxation pathway leads from the S1 minimum via vibronic coupling to the S2 potential well followed by fast inter-system crossing to the T2 state. For an estimate of individual rate constants a quantum dynamical treatment will be required. The global minimum of the T1 surface has a chair-like nuclear conformation and corresponds to the T1 (1 3B2, piHOMO-->pi) electronic structure. Phosphorescence is weak here with a calculated radiative lifetime of 0.59 s. For the second potential well on the T1 surface with T3 (1 3B1, piHOMO-->sigma*) electronic structure, nonradiative processes are predicted to dominate the triplet decay.     

Comprehensive theoretical studies on the low-lying electronic states of NiF, NiCl, NiBr, and NiI

The low-lying electronic states of the nickel monohalides, i.e., NiF, NiCl, NiBr, and NiI, are investigated by using multireference second-order perturbation theory with relativistic effects taken into account. For the energetically lowest 11 lambda-S states and 26 omega states there into, the potential energy curves and corresponding spectroscopic constants (vertical and adiabatic excitation energies, equilibrium bond lengths, vibrational frequencies, and rotational constants) are reported. The calculated results are grossly in very good agreement with those solid experimental data. In particular, the ground state of NiI is shown to be different from those of NiF, NiCl, and NiBr, being in line with the recent experimental observation. Detailed analyses are provided on those states that either have not been assigned or have been incorrectly assigned by previous experiments.     

Mg2H2: new insight on the Mg-Mg bonding and spectroscopic study

The six dimensional potential energy surface of the electronic ground state X?(1)Σ(g)(+) of Mg(2)H(2) has been generated by the coupled-cluster approach with single, double and perturbative triple excitations [CCSD(T)] combined with the aug-cc-pCVTZ basis set for Mg atoms and the aug-cc-pVTZ basis set for the H atoms. The analytical representation of this surface was used in variational calculations of the rovibrational energies of Mg(2)H(2), Mg(2)D(2), and HMg(2)D for J = 0 and 1. For Mg(2)H(2), the rotational constant B(0) is computed to be 0.1438 cm(-1), and the fundamental anharmonic wavenumbers are calculated to be ν(1) = 1527.3 cm(-1) (Σ(g)(+)), ν(2) = 275.3 cm(-1) (Σ(g)(+)), ν(3) = 1503.6 cm(-1) (Σ(u)(+)), ν(4) = 312.9 cm(-1) (Π(g)), and ν(5) = 256.5 cm(-1) (Π(u)). In addition, the electronic ground states of Mg(2)H, MgH(2), Mg(2), and MgH have been investigated in order to compute the bonding energies of Mg(2)H(2) and to explain the strength of the Mg-Mg bond in this tetra-atomic molecule. The nature of the low-lying excited states of Mg(2)H(2) is also studied.     

Inversion vibration of PH3+(X2A2") studied by zero kinetic energy photoelectron spectroscopy

We report the first rotationally resolved spectroscopic studies on PH3+(X2A2") using zero kinetic energy photoelectron spectroscopy and coherent VUV radiation. The spectra about 8000 cm(-1) above the ground vibrational state of PH3+(X2A2") have been recorded. We observed the vibrational energy level splittings of PH3+(X2A2") due to the tunneling effect in the inversion (symmetric bending) vibration (nu2+). The energy splitting for the first inversion vibrational state (0+/0-) is 5.8 cm(-1). The inversion vibrational energy levels, rotational constants, and adiabatic ionization energies (IEs) for nu2+ = 0-16 have been determined. The bond angles between the neighboring P-H bonds and the P-H bond lengths are also obtained using the experimentally determined rotational constants. With the increasing of the inversion vibrational excitations (nu2+), the bond lengths (P-H) increase a little and the bond angles (H-P-H) decrease a lot. The inversion vibrational energy levels have also been calculated by using one dimensional potential model and the results are in good agreement with the experimental data for the first several vibrational levels. In addition to inversion vibration, we also observed firstly the other two vibrational modes: the symmetric P-H stretching vibration (nu1+) and the degenerate bending vibration (nu4+). The fundamental frequencies for nu1+ and nu4+ are 2461.6 (+/-2) and 1043.9 (+/-2) cm(-1), respectively. The first IE for PH3 was determined as 79670.9 (+/-1) cm(-1).     

Resonance spectrum and dissociation dynamics of ozone in the 3B2 electronically excited state: experiment and theory

The rovibrational spectrum assigned to the low-lying (3)B(2) electronic state of ozone is measured with intracavity laser absorption spectroscopy. The experimental results are interpreted by means of quantum dynamical calculations on a global ab initio potential energy surface. The observed spectrum is shown to originate from the vibrational ground state in the local minimum of the (3)B(2) potential. The spectrum of short-lived resonance states in this local minimum is analyzed. Additionally, the global minimum of the surface is shown to lie in the dissociation channel in the van der Waals region. This region supports a short sequence of weakly bound vibrational states.