[en] All interatomic distances [D(calc.)_j] in Pbnm silicate olivines are linearly related with M1 and M2 site occupancy through a relationship of the type: D(calc.)_j = Σ_sΣ_iωsub(ij_s)Xsub(i_s) + ξ_j, where ωsub(ij_s), ξ_j are adjustable coefficients, and Xsub(i_s) are the fractions of ith ion in site s. The precision attained by this relation, based on seven divalent ions (Mg, Fe, Ca, Mn, Co, Ni, Zn), is satisfactory, the mean difference vertical strokeD(calc.) - D(obs.)vertical stroke always being less than 0.005 A for each distance. Moreover, all ωsub(ij_s) coefficients are related to properties of ions through a relation of the type: ωsub(ij_s) = K1sub(j_s)(Σ^Z_m=1I_m)_i^-1/2+K2sub(j_s)α_i^f1/4 + K3sub(j_s), where Σ^Z_m=1I_m is the sum of the ionization potentials for the ith ion up to its valency state (Z), α_i^f is its polarizability, and K1sub(j_s), K2sub(j_s) and K3sub(j_s) are numerical constants. The existence of this strict dependency is predictable, based on the concept of effective nuclear charge and its relationship with polarizability and ionic potentials. As a consequence, all interatomic distances may be simulated through an equation of the type: D(calc.)_j = Σ_S{W1sub(j_s)Σ_i[Xsub(i_s)(Σ^Z_m=1I_m)_i^-1/2]} + Σ_s[W2sub(j_s)Σ_i(Xsub(i_s)α_i^f1/4)] + W3_j, where W1sub(j_s), W2sub(j_s) and W3_j are adjustable parameters which directly involve the ionization potentials and polarizabilities of the ions. (orig.)

[en] Published in summary form only

No abstract available

[en] A semiempirical method for calculating the polarizability of diatomic molecules in the entire range of possible values if their internuclear distance is proposed. The method is based on the functional dependence of the polarizability of a molecule on the internuclear distance R in the region of small R obtained in the previous paper, the known polarizabilities and their derivatives at the equilibrium position of the molecule nuclei, and also results of the model of polarized of atoms valid for large internuclear distances. The efficiency of the proposed method is tested for the hydrogen molecule for which reliable polarizability values are available in the wide range of internuclear distances. The proposed method is used for calculating the polarizabilities of the nitrogen and oxygen molecules. 17 refs., 6 figs., 1 tab

[en] An accurate Patterson function, free of artifacts, is obtained by transforming low-energy electron diffraction I-V spectra at multiple incident angles. The demonstration is carried out using normal incidence measured spectra and calculated spectra at three angles of incidence. The errors between intensity spots in the Patterson function and known interatomic distances are less than 0.01 {angstrom} in the horizontal direction and 0.09 {angstrom} in the vertical direction. The reason for the high accuracy in the horizontal direction is given

[en] The interatomic distances in the transition states of radical hydrogen atom abstraction reactions X^.+HY → XH+Y^. determined by quantum chemical calculations are systematized and generalized. It is shown that depending on the reaction centre structure, these reactions can be subdivided into classes with the same X...Y interatomic distance in each class. The transition state geometries found by the methods of intersecting parabolas and intersecting Morse curves are also presented. The X...H...Y fragments are almost linear, the hydrogen atom position being determined by the reaction enthalpy. The effects of triplet repulsion, electronegativities and radii of X and Y atoms, the presence of adjoining π-bonds, and steric effects on the X...Y interatomic distances are analyzed and characterized. The bibliography includes 62 references.

[en] The B0_u⁺-X0_g⁺ and B1_u-X1_g transitions of ⁸⁰Se₂ and ⁷⁸Se₂ are reinvestigated. Several new bands are reported, especially for the B1_u-X1_g system, their vibrational numbering being confirmed by isotope shift studies. The Franck-Condon factors and r-centroid values are evaluated. By correlating the theoretically computed intensities with observed values, the internuclear distance dependence of the electronic transition moments of these two systems is determined for the first time

No abstract available

[en] The parameters needed to calculate bond valences from bond lengths have been determined for 750 atom pairs using the Inorganic Crystal Structure Database. The most accurate 141 are listed and an algorithm is given which allows the calculation of the remainder as well as the calculation of parameters for over a thousand other bond types. Graphical bond-valence-bond-length correlations are presented for hydrogen bonds. (orig.)

[en] The crystal structure of scandium dodecaboride is determined. The data obtained have confirmed that ScB₁₂ has cubic f.c.c. structure, a=0.7402(3) nm. The results unambiguosly testify to the fact that ScB₁₂ structure belongs to the UB₁₂ type