BeH2(X1Σ+g)与H2S(X1A1)分子的结构与解析势能函数

运用单双取代二次组态相关(QCISD)方法,在6-311++G(3df,3pd)基组水平上,对BeH₂和H₂S分子的结构进行了优化计算,得到基态BeH₂分子的稳定结构为D_∞h构型,电子态为X¹Σ⁺_g,平衡核间距R_BeH=0.13268nm,R_{关键词： 2}')" href="#">BeH₂ 2S')" href="#">H₂S Murrell-Sorbie函数 多体项展式理论 解析势能函数     

Exploration of large amplitude motions in the Ca+Ar2 complex

ABSTRACT

We present a theoretical study of the ground electronic state potential of the Ca⁺Ar₂ complex and of its photoabsorption spectra, simulated at temperatures ranging between 20 and 220?K. These calculations exploit a Monte-Carlo (MC) method, based on a one-electron pseudo-potential approach. A pairwise additive potential fitted to coupled cluster ab initio points, is used to model the Ca⁺Ar₂ complex. Our study shows that the most stable form of Ca⁺Ar₂ is a bent C_2v structure, whereas the linear isomer is located at around 90?±?10?cm^?1 above in energy. The analysis of the photoabsorption spectra establishes that a structural transition from bent Ca⁺Ar₂ to linear ArCa⁺Ar occurs at T～100?K. Trends in binding energies of both isomers, bond lengths and bond angles are also discussed. Molecular orbital overlaps provide an explanation for the order of stability between the bent and linear structures.     

A theoretical study of the lowest 2 B 1, 2 A 1 and 2 B 2 electronic states in H2S+ and a comparison with corresponding states in related systems

Large scale configuration interaction calculations are employed to study the potential energy surfaces of the three lowest lying states in H₂S⁺. The calculated structural data for the X ² B ₁ and A ² A ₁ states are in very good agreement with previous evidence, but the ² B ₂ state is found to exhibit an [S---H₂]⁺ structure with large SH bond separations and a very small internuclear angle of 32°. Energies and wavefunctions are calculated for all three vibrational modes in the X ² B ₁ and A ² A ₁ excited states of H₂S⁺ and D₂S⁺ and the corresponding Franck-Condon factors for the A ² A ₁-X ² B ₁ band are determined; a maximum in absorption intensity is predicted to occur for v′₂ = 5–6 in H₂S⁺ and for v′₂ = 7–8 in D₂S⁺ for the A ² A ₁-X ² B ₁ transition, for which the calculated T ₀ energy of 18 620 cm^-1 is in excellent agreement with the experimentally determined value of 18 520 cm^-1. Extensive comparison is made with the other AH₂ systems PH₂, NH₂ and H₂O⁺ and trends with respect to geometry, vertical excitation and ionization energies as well as vibrational structure are pointed out; for this purpose the ² B ₂ potential energy curve of PH₂ has also been calculated.     

Hyperfine structure in the BΠ0u state of Br2 and the influence of the perturbing 1u state

Using Doppler-free polarization spectroscopy, the hyperfine structure of the B-X system of ⁷⁹Br₂ was measured for the levels B³Π_0⁺u, v′ = 16–28, and X¹Σ_g⁺, v″ = 1, 2. Besides the nuclear electric quadrupole coupling, the magnetic spin-rotation interaction was analyzed, which varies strongly with the vibrational energy of the electronically excited state. This behavior originates from a perturbing repulsive state Ω = 1_u, the potential of which can be estimated in this way.     

High-resolution infrared spectrum of acetylene in the region of the bending fundamental v 5

The infrared spectrum of C₂H₂ in the region of the bending fundamental v ₅ has been studied at a resolution of about 0·015 cm^-1. The molecular constants G ₀(v ₅=1) = 730·3341 (1) cm^-1 and B ₀ = 1·176641 (2) cm^-1 have been derived. In addition to the fundamental, all the hot bands starting from the levels v ₄ and v ₅ have been investigated. The vibrational, vibration-rotation coupling and centrifugal constants for the excited vibrational states v ₅ = 2 and v ₄ = v ₅ = 1 have been derived using the vibration-rotation energy matrix.     

Electron paramagnetic resonance of deep boron acceptors in 4H-SiC and 3C-SiC crystals

EPR spectra of deep boron in 4H-SiC and 3C-SiC crystals have been observed and studied. Two sites in 4H-SiC produced deep-boron EPR signals, quasi-cubic k and hexagonal h. In both cases the deep-boron center symmetry is close to axial along the c crystal axis, and the g factor anisotropy is about an order of magnitude larger than that for shallow boron centers. In the 3C-SiC crystal, the deep-boron symmetry is also close to axial along one of the four 〈111〉 directions. The model proposed for the deep boron center with acceptor properties is B_Si-v _C, where B_Si is the boron substituting for silicon, and v _C is the carbon vacancy, with the B_Si-v _C direction coinciding in 4HSiC with the hexagonal axis of the crystal for both k and h positions. In the cubic 3C-SiC crystal, there are four equivalent deep boron centers, which represent B_Si-v _C pairs with the bond directed along one of the four 〈111〉 crystal directions. Fiz. Tverd. Tela (St. Petersburg) 40, 36–40 (January 1998)     

Theoretical study of molecular properties of low-lying electronic excited states of H2O and H2S

Geometries, excitation energies, dipole moments and dipole polarisability tensor components of the ground and four lowest excited states ³ B ₁, ¹ B ₁, ³ A ₂, ¹ A ₂ of the H₂O and H₂S molecules were calculated at the CASSCF, CASPT2, CCSD and CCSD(T) level of approximation. Vertical excitation and equilibrium transition energies of these states, having the Rydberg character, are reported too. Properties of both molecules in the ground and in low lying excited states are compared and discussed from the point of view of their molecular electronic structure. Upon excitation we observe dramatic changes of dipole moments and polarisabilities with respect to the ground state. We stress the change of the polarity of H₂O in all excited states accompanied by the enhancement of the dipole polarisability by an order of magnitude. Large, even if less pronounced, are changes of electric properties of H₂S in its excited states. Dipole moments and dipole polarisabilities of ³ B ₁, ¹ B ₁ states of H₂S and H₂O behave quite analogously in comparison to their respective ground state. The general pattern of properties for both molecules in their ³ A ₂ and ¹ A ₂ excited states is more different due to a pronounced participation of the sulphur d-orbitals in these states of the H₂S molecule.     

Theoretical study on the Cope rearrangement mechanisms and the homoaromaticity of semibullvalene,barbaralane, and 1,5‐methanosemibullvalene

Cope rearrangement mechanisms and the homoaromaticity of semibullvalene, barbaralane, and 1,5‐methanosemibullvalene in the ground and lowest excited states were studied by ab initio methods. In the ground state, the rearrangement reactions of semibullvalene and barbaralane occurred concertedly through the transition states with C_2v symmetry, and the transition states had a homoaromatic nature. In particular, the transition state of barbaralane exhibited the strongest homoaromaticity among the three systems treated here. On the other hand, for 7,8‐methanosemibullvalene, the structure with C_2v symmetry was not a transition state but one with a stable energy minimum. The energy minimum structure with C_2v symmetry had a biradical character. The lowest excited states of semibullvalene and barbaralane were the excitation to the σ* anti‐orbital, ¹B₂ and ¹B₁ states, and led to near di‐allyl states. The lowest excitation state of 1,5‐methanosemibullvalene had C_s symmetry and was the A″ state excitation in one side of two allyl parts. Copyright © 2011 John Wiley & Sons, Ltd.     

An ab initio investigation of the low-lying electronic states of BeH

Potential energy curves(PECs) for the ground state(X 2 Σ +) and the four excited electronic states(A 2 Π,B 2 Π,C 2 Σ +,4 Π) of a BeH molecule are calculated using the multi-configuration reference single and double excited configuration interaction(MRCI) approach in combination with the aug-cc-pVTZ basis sets.The calculation covers the internuclear distance ranging from 0.07 nm to 0.70 nm,and the equilibrium bond length R e and the vertical excited energy T e are determined directly.It is evident that the X2Σ+,A2Π,B2Π,C2Σ+ states are bound and 4Π is a repulsive excited state.With the potentials,all of the vibrational levels and inertial rotation constants are predicted when the rotational quantum number J is set to be equal to zero(J = 0) by numerically solving the radial Schr¨odinger equation of nuclear motion.Then the spectroscopic data are obtained including the rotation coupling constant ω e,the anharmonic constant ωexe,the equilibrium rotation constant Be,and the vibration-rotation coupling constant αe.These values are compared with the theoretical and experimental results currently available,showing that they are in agreement with each other.     

MgH分子X2Σ+，A2Π和B2Σ+电子态的势能函数

利用QCISD(T),SAC-CI方法和cc-pVQZ,aug-cc-pVTZ,6-311++G及6-311++G(3df,2pd)基组,对MgH分子的基态X²Σ⁺,第一简并激发态A²Π和第二激发态B²Σ⁺的结构进行优化计算.通过对4个基组计算结果进行比较,得出6-311++G(3df,2pd)基组为最优基组.使用 关键词： 分子结构与势能函数 激发态 Murrell-Sorbie函数 C₆函数')" href="#">Murrell-Sorbie+C₆函数     

SiX2(X=H，F)分子的结构与势能函数

应用QCISD/6-311++G(3df,3pd)和B3P86/6-311++G(3d2f)对SiH₂,SiF₂的结构进行了优化,优化出SiH₂分子的稳定构型为C_2v,电子态为¹A₁,其平衡核间距R_e=0.15149nm、键角∠HSiH=92.5025°、离解能为3.7098eV. SiF _{关键词： 2}')" href="#">SiH₂ 2')" href="#">SiF₂ 多体项展式理论 势能函数     

A quasiclassical study of collisions of He with HD(B 1Σ+ u )

A quasiclassical trajectory study has been carried out for collisions of ⁴He with electronically excited H₂(B ¹Σ⁺ _u ) and its isotopomer HD. By using analytical fits for the ab initio potential energy surfaces of the ground and the excited state we have obtained vibrational and electronic quenching cross sections for several initial conditions. We draw the following conclusions. Vibrational excitation strongly promotes electronic quenching whereas translational energy is less effective. Rotational excitation decreases the rate of quenching. In a remarkable contrast to the ground electronic state, vibrational energy transfer on the excited potential energy surface is an efficient and fast process. Collisions at high energies results in T → R energy transfer. The above conclusions are valid for both H₂ and HD.     

Structures and stabilities of endo- and exohedral Si20H20 derivatives: X@Si20H20 and XSi20H20, X = H + , H,N, P,C − , and Si −

Geometries, relative energies, and stabilities of endo- and exohedral complexes, X@Si₂₀H₂₀ and XSi₂₀H₂₀, (X = H⁺, H, N, P, C^?, and Si^?) are calculated at B3LYP/6-31G* level. The energy minimum structure of Si₂₀H₂₁ ⁺ shows that the proton cannot be positioned in the Si₂₀H₂₀ centre, but prefers attach to Si₂₀H₂₀ exohedrally with C_2v symmetry. Most investigated I_h endohedral complexes X@Si₂₀H₂₀ (X = H, N, P, C^?, and Si^?) are local minima, except for ²N@Si₂₀H₂₀, which is a high-order saddle point. Inclusions energies of the endohedral complexes are calculated, and it reveals that energy penalties caused by encapsulation are rather small. Exohedral complexes XSi₂₀H₂₀ (X = H, N, P, C^?, and Si^?) have C_2v or C_s local minima, and most of them are more stable than their endohedral isomers with the exception of C_2v ⁴PSi₂₀H₂₀ and ⁴Si^?Si₂₀H₂₀.     

B2C(1A1)和BC2(2A′)的结构与解析势能函数

采用单双取代的二次组态相互作用方法，分别选用6-311++G(d,p)和6-311G(df,pd)基组，对B₂C和BC₂分子的结构进行了优化，得到这两个分子的基态结构为C_2v和C_s，基态电子状态为¹A₁和²A′，同时还得到了它们的平衡几何结构、离解能、谐振频率和力常数. 关键词： 碳化硼 Murrell-Sorbie函数 谐振频率 势能函数     

Analytical potential energy functions for the ground and some excited states of N2

The analytical potential energy functions have been calculated for the ground state X¹Σ⁺_g and four excited electronic states a¹Π_g, A³Σ⁺_u, B′³Σ^?_u and B³Π_g of N₂ molecule using the algebraic and energy-consistent methods (AM-ECM). Based on our previously published full AM vibrational energies and spectroscopic constants, the low-lying force constants f_n, the expansion coefficients a_n and the variational parameters λ in the AM–ECM potentials are determined for these states. The computed AM–ECM potential energy curve of each state is in excellent agreement with the experimental data and better than other analytical potentials.     

Non-adiabatic potentials for H2 +

In principle exact non-adiabatic pseudo-potentials for H₂ ⁺ and D₂ ⁺ are formulated in terms of the theory of conditional probability amplitudes in wave mechanics. Numerical results for the v = 0 and v = 1 (J = 0) states of H₂ ⁺ are derived from previously computed accurate non-adiabatic wave-functions. These results indicate that the non-adiabatic pseudo-potentials only differ from the adiabatic potential by small energies of the same magnitude as the non-adiabatic corrections to the adiabatic energy levels.     

1,4-二氧六环的真空紫外同步辐射光解离电离研究

The photoionization and photodissociation of 1,4-dioxane have been investigated with a reflectron time-of-flight photoionization mass spectrometry and a tunable vacuum ultraviolet synchrotron radiation in the energy region of 8.0-15.5 eV. Parent ion and fragment ions at m/z 88, 87, 58, 57, 45, 44, 43, 41, 31, 30, 29, 28 and 15 are detected under supersonic conditions. The ionization energy of DX as well as the appearance energies of its fragment ions C₄H₇O₂⁺, C₃H₆O⁺, C₃H₅O⁺, C₂H₅O⁺, C₂H₄O⁺, C₂H₃O⁺, C₃H₅⁺, CH₃O⁺, C₂H₆⁺, C₂H₅⁺/CHO⁺, C₂H₄⁺ and CH₃⁺ was determined from their photoionization efficiency curves. The optimized structures for the neutrals, cations, transition states and intermediates related to photodissociation of DX are characterized at the B3LYP/6-31+G(d,p) level and their energies are obtained by G3B3 method. Possible dissociative channels of the DX are proposed based on comparison of experimental AE values and theoretical predicted ones. Intramolecular hydrogen migrations are found to be the dominant processes in most of the fragmentation pathways of 1,4-dioxane.     

The structure and the analytical potential energy function of NH2 （X^2B1）

This paper reports that the equilibrium structure of NH2 has been optimized at the QCISD/6-311＋＋G （3df, 3pd） level. The ground-state NH2 has a bent （C2v, X^2B1） structure with an angle of 103.0582°. The geometrical structure is in good agreement with the other calculational and experimental results. The harmonic frequencies and the force constants have also been calculated. Based on the group theory and the principle of microscopic reversibility, the dissociation limits of NH2（C2v, X^2B1） have been derived. The potential energy surface of NH2（X^2B1） is reasonable. The contour lines are constructed, the structure and energy of NH2 reappear on the potential energy surface.