1,720,991 research outputs found
The effect of the solvent in electronic transitions: some recent developments in the continuum model
No full textA recently proposed method to deal with absorption/emission transitions in solution is summarized. Attention is focused on the evaluation of relative energies in vertical excitation processes as well as on thermodynamic considerations about the energetics of the solution. A numerical example relating to the spectrum of CH3CHO in aqueous solution is presented and discussed
evaluation of absorption and emission transitions for molecular solutes, including separate consideration of orientational and inductive solvent effects
No full textAn ab initio computation procedure to obtain electronic transition wave numbers in solution is presented and discussed. The continuum description of the bulk solvent is adopted, and solute–solvent interaction is reduced to a closed-form interaction operator added to the solute Hamiltonian. The resulting Schrödinger equations are solved variationally. No limitations are imposed on the shape of the solvent cavity or on the level of accuracy of the ab initio procedure
On the free energy changes of a solution in light absorption or emission processes
No full textA simple model to evaluate energy changes in dilute solutions produced by absorption or emission of light is proposed. The computational scheme exploits some characteristics of the continuum model of liquids and is inserted into ab initio quantum-mechanical programs for isolated molecules. The model is addressed to evaluate changes in thermodynamic properties of the whole solution — while earlier models often consider the solute only — and it presents a detailed decomposition of the phenomenon into successive steps
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Multipole expansions of the electrostatic molecular potential
No full textMultipole expansions of the electrostatic molecular potential up to the hexadecapole terms are examined for H20, NH 3 and C2H~NH. A reasonable approximation to get unexpensive first order
representations of the electrostatic potential for regions outside the van der Waals volume is found
The mechanism of carbonyl reduction by LiBH_4 : an ab initio investigation with inclusion of solvent effects
No full textThe mechanism of the reaction H2CO + LiBH4 → products has been investigated by using SCF calculations in a modified formalism which includes solvent effects. The effects of the solvent are represented by a one-electron operator added to the Fock Hamiltonian of the molecular system. The influence of the solvent on the reaction energy profile, on the geometry of the transition state, intermediate species, reagents and products is brought out by comparing the results with similar ones referring to the same reaction in vacuo (J. Mol. Struct., Theochem, 87 (1982) 181). Attention is paid to alternative mechanisms involving ionic dissociation of the reactant
Structure and thermal E-Z isomerization of substituted 4-Phenylimino-5-pyrazolones and hexafluoroacetones anils
No full textThe structure of the title compounds was examined by means of ab initio MO theory employing the STO-3G basis set. The optimized geometries represent a good basis for the discussion of conformation and configuration of these molecules. A quantum-chemical solvation model was applied for the estimation of the solvent influence. Dependent on the extent of push-pull conjugation in the investigated systems, the conformation of the linear inversion state, which has to be passed during the isomerization process, changes between a planar and perpendicular orientation of the N-phenyl ring. These conformation differences could be responsible for deviations of Hammett plots of the isomerization rate from linearity for special groups of aromatic azomethines
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