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1.
《Chemical physics letters》1985,116(6):482-486
Binding energies and stabilities of Na+ with bidentate ethylene diamine were studied using ab initio MO calculations with a 6-31G* basis set. The computed results for bidentate ethylene diamine were compared with those for two (monodentate) CH3NH2 molecules.  相似文献   

2.
The He l, He II and Ne I photoelectron (p.e.) spectra of thiazyl fluoride. NSF, are compared with ab initio LCAO MO SCF calculations via Koopmans' theorem. The calculations predict the valence formulation NSF, and the p.e. spectrum is consistent with this. Comparisons are drawn with the isoelectronic molecule SO2  相似文献   

3.
Self-consistent fieldab initio calculations have been performed for CH3Br. The calculated equilibrium conformation is in good agreement with experiment. Valence and core level ionization potentials, Mulliken population analysis and electronic properties are presented. The ionization potentials are in good agreement with the experimental values, except for one case in which the experimental value may be wrongly assigned. The calculated dipole moment, 2.43 Debye, is 34% or 0.6 Debye larger than the experimental value.Two of us (C.W.B. and G. del C.) wish to acknowledge the hospitality of the IBM San José Research Laboratory and joint study agreements between the IBM and the Lawrence Berkeley Laboratory and the National University of Mexico respectively.  相似文献   

4.
The valence isomerization of the 1,2-dithiete parent compound to the open-chain dithial was studied by CASSCF multiconfiguration methods including the CASPT2 perturbational treatment. The isomerization energy remains small at the highest level of theory. In agreement with Jonas and Frenking, the cyclic structure is only then preferred over the acyclic ones if f-functions on the sulfur atoms are considered. If they are included, the 1,2-dithiete is more stable by 3.8 kcal/mol and the barrier amounts to 24.9 kcal/mol at the CASPT2(8,8)/6-31G(2df)//MP2/6-31G* level of theory. According to MP2/6-31G* geometry optimizations, substitution of H by NH2 and CH3 reduces the stability of the 1,2-dithiete ring structures relative to the open-chain dithiocarbonyl structures, whereas the inverse holds for acceptor substitution by CN and CF3. A higher stability of benzodithiete relative to ortho-dithiobenzoquinone is predicted at all employed levels of theory. This is in good agreement with conclusions drawn from experimental results. Whereas the experimental microwave geometry of 1,2-dithiete is well reproduced theoretically, the experimental electron diffraction geometry of 3,4-bis-(trifluoromethyl)-1,2-dithiete differs from the calculated one. © 1996 John Wiley & Sons, Inc.  相似文献   

5.
Ab initio calculations on the isomerization of butene and pentene radical cations indicate that, for all classical ion structures, the lowest barrier for a rearrangement to the most stable ion structure is below the dissociation limit. Isomerizations of linear butene radical cations to the isobutene structure take place via the CH3CC2H5·+ structure, whereas in the pentene case the connection between linear and branched ion structures proceeds via the 1,2-dimethylcyclopropane radical cation. From the results a qualitative model is derived which suggests that for larger alkene radical cations an isomerization to structures with four alkyl substituents on the double bond may be in close competition with dissociation.  相似文献   

6.
Experiments show changes in the carbon-oxygen bond lengths when a carboxylic acid dimerizes. To see how these changes are depicted in the electronic structure, a series of ab initio calculations have been made on monomeric and dimeric formic acid. Both systems have been examined through energy optimalization and through a Mulliken population analysis.The experimental changes can be qualitatively explained by the calculations, however, the quantitative agreement is not as good as desired.The calculations on monomeric formic acid give valuable information on the possibility of separately computing the different structural parameters.  相似文献   

7.
For the CF, PF, SF, and MoF ions appearing after the F1s photoionization, the possibility of dissociation has been shown by the ab initio MO LCAO method within the Z + 1 core equivalent model. According to the calculations, the decay channel AF → AF + F(1s12p6) is energetically open for the ions. So the interpretation of the gas-phase emission FKα spectra, in which the bands are assigned to the discrete transition energies, can be unacceptable for these ions. The conditions and signs of such failure are discussed.  相似文献   

8.
9.
Ab initio calculations are reported for cis and trans butadiene and some of their ions. The calculations are compared with semi-empirical results, and used to predict coupling constants.  相似文献   

10.
Ab initio calculations at the MRCI//ROHF/6-31G** level suggest that the 1,5-hexadiyne radical cation is not stable and isomerizes to the 1,2,4,5-hexatetraene radical cation without a barrier. After this rearrangement, the internal energy of the ions will be sufficient for a subsequent isomerization to the benzene structure. At energies of about 1 eV above the vertical ionization energy, the 1,5-hexadiyne radical cation may dissociate to linear neutral and ionic C3H3 fragments. These results are in excellent agreement with previous experiments.  相似文献   

11.
The magnetic hyperfine coupling constants in NO2 and CO2? have been computed by an initio methods. Spin annihilation is found to be essential in order to obtain useful results for the dipolar couplings, but has much less influence on the isotropic couplings. The electric quadrupole coupling constants have also been evaluated, and are in good agreement with available experimental data.  相似文献   

12.
Self-consistent-field calculations are reported on the ethylene and fluoroethylene molecules. A comparative analysis of the two molecules shows that the effects of substituting a hydrogen atom with a fluorine atom in ethylene are fairly local. Ionization potentials in the ethylene molecule are calculated. The effects of hydrogen p-functions are studied in both molecules, and these effects are found to be rather small, particularly in fluoroethylene. A number of molecular properties are reported for both molecules.
Zusammenfassung Für Äthylen und Fluoroäthylen werden SCF-Rechnungen durchgeführt. Eine vergleichende Analyse der beiden Moleküle zeigt, daß die Effekte der Substitution eines Wasserstoffatoms durch Fluor in Äthylen ziemlich lokal begrenzt sind. Die Ionisationspotentiale für Äthylen werden berechnet. Die Auswirkung von Funktionen am Wasserstoffatom werden in beiden Molekülen untersucht; sie sind relativ gering, besonders im Fluoroäthylen. Eine Reihe von molekularen Eigenschaften wird für beide Moleküle angegeben.

Résumé Calculs SCF sur l'éthylène et le fluoroéthylène. Une analyse comparée des deux molécules montre que les effets de la substitution d'un atome d'hydrogène par un atome de fluor dans l'éthylène sont pratiquement locaux. Les potentiels d'ionisation de la molécule d'éthylène sont calculés. L'effet de l'introduction de fonctions p sur l'hydrogène est étudié dans les deux molécules; on le trouve faible, en particulier dans le fluoroéthylène. Etude de quelques autres propriétés moléculaires.
  相似文献   

13.

Abstract  

The dissociation of 1,3-cyclobutanedione radical cation was studied by ab initio direct classical trajectory calculations at the BH&HLYP/6-31G(d) level of theory. A microcanonical ensemble using normal mode sampling was constructed by distributing 10 kcal/mol of excess energy above the transition state for the tautomerization of the keto-enol to the diketo form. A total of 210 trajectories were run starting from this transition state, yielding chemically activated 1,3-cyclobutanedione radical cation. The majority of the trajectories resulted in CH2CO + CH2CO, with the activated CC bond breaking nearly twice as often as the spectator CC bond. The non-statistical behavior is observed because the rate of energy redistribution within the molecule is comparable to or slower than the dissociation rates. In addition to the expected products, dissociation to CH2COCH2 + CO and formation of a proton-transferred product HCCO· + CH3CO+ were also seen in some of the trajectories.  相似文献   

14.
The excited states of the permanganate and chromate ions are described by better-than-minimal basis set SC FMO CI calculations. The results are compared with the experimental absorption spectra.  相似文献   

15.
17O NMR chemical shifts and calculated (ab initio MO theory) electron densities are reported for a series of para-substituted acetophenones, X? C4H6? COCH3, where X = NH2, OCH3, F, Cl, CH3, H, COCH3, CN, NO2. The 17O shifts are very sensitive to the para substituent and cover a range of some 51 ppm. Donors induce upfield shifts and acceptors downfield shifts. The substituent chemical shifts (SCS) correlate precisely with σI and σR+ using the Dual Substituent Parameter (DSP) method. The derived transmission coefficients ρI and ρR indicate that polar and resonance mechanisms contribute approximately equally to the observed substituent effects. The shifts also correlate well with calculated π-electron densities (slope = 1500 ppm per electron) confirming their electronic origin. λ values are also reported, and the role of the average excitation energy, ΔE, in determining 17O SCS values is discussed. It is concluded that variations in ΔE are minor and that the local Δ-electron density is the dominant feature controlling 17O SCS values.  相似文献   

16.
The hydration energies for the NH+4 and CH3NH+3 ions were calculated by an ab initio MO method. The aqueous solvation energy difference between these two ions was found to be accounted for by the interactions of the ions with a few solvent molecules.  相似文献   

17.
18.
Ab initio orbital calculations on phenol, nitrobenzene, and 2-nitroresorcinol have been performed with the GAUSSIAN 92 series of programs. Initial RHF/6-31G* and RHF/6-31G** optimizations were followed by second-order MØller-Plesset MP2(FC)/6-31G* optimizations. The general geometrical features of these molecules, and, in particular, the characteristic changes as going from phenol to 2-nitroresorcinol and from nitrobenzene to 2-nitroresorcinol are in good agreement with recent gas-phase electron diffraction studies and with the notion of resonance-assisted intramolecular hydrogen-bond formation in 2-nitroresorcinol.  相似文献   

19.
The application of MO LCAO methods to molecules containing elements in the higher periods is discussed, especially compounds containing two phenyl rings linked via an oxygen atom. The calculated -electron density is found to agree with the observed electronic absorption spectra, dipole moment, effects of polarity on reactivity, and so on, provided that the wave function used for the heteroatom with n>2 is =c1 npz+ +c2 nd+...; the terms c2 nd... provide correction for the change in the atomic function npz produced by the surrounding atoms. This effect is not important for O, N, and C (first period). The effects of surrounding atoms on npz for the halogen atom have evidently to be considered in computations on the -electron density for any molecule containing such an atom.  相似文献   

20.
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