The study of rotational mobility of stable nitroxyl radicals in polyvinylacetate

Analyses of the rotational diffusion characters of free and bonded nitroxyl radicals in polyvinylacetate were carried out. The radical rotational character essentially depends on the molecular sizes of the radicals. The movement of the “small” radical is matched by the arbitrary jump tumbling model. The rotation of the “large” radical (both probe and label) occurs by the Brownian rotational diffusion mechanism. The correlation times in the slow-motion region are calculated by taking into account the radical rotation mechanism. Comparison of the τ_c values for the free and bonded radicals with those obtained by the NMR technique shows that movements of the spin probes and labels depend not only on the short polymer segments but on other factors also.     

Interactions in open-shell clusters: ab initio study of pre-reactive complex O(3P) + HCl

Van der Waals interactions between the ground-state triplet O(3P) atom and the closed-shell HCl molecule are investigated in the pre-reactive region. Three adiabatic (two of A' symmetry and one of A' symmetry) and four non-relativistic diabatic potential energy surfaces are obtained by combining a restricted open-shell coupled cluster approach with the multireference configuration interaction method. The lower A' adiabatic potential surface has a single minimum (D(e) = 589 cm(-1)) for a linear O...HCl configuration. The upper A' potential has a weak (D(e) = 65 cm(-1)) minimum for a linear HCl...O configuration. The A' adiabatic potential has a weak (124 cm(-1)) T-shaped minimum. Adiabatic potentials intersect once in the O...HCl linear configuration and twice in the linear HCl...O geometry. The role of electrostatic interactions in shaping these potentials is discussed. The effects of spin-orbit coupling on this interaction are also investigated assuming a constant value of the SO parameter.     

Magnetic organometallosiloxanes

The generalized analysis of a change in magnetic properties of organometallosiloxanes as a function of the number of metal atoms in their molecules (on going from mono- and binuclear to polynuclear crystalline and polymeric compounds) is presented. The relation between the magnetic characteristics and structural parameters of metal-containing fragments is studied. The factors affecting the formation of exchange-coupled ionic pairs and clusters in polymeric systems are analyzed. The ways to the organization of magnetic phases in polymeric systems are considered: the choice of conditions of chemical synthesis, the organization of metal atoms in a common spin system upon incorporation of conducting coordinating additives, and thermocondensation and reduction processes leading to the formation of a metallic phase dispersed in a silicon dioxide matrix. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 8, pp. 1432–1442, August, 1997.     

Direct one-index transformations in multiconfiguration response calculations

The evaluation of gradient vectors of a general operator with one-index, double-one-index, or higher-order one-index transformed integrals is a key operation in multiconfiguration response theory calculations. We describe an integral-driven direct algorithm that carries out this operation efficiently without pretransforming the integrals. The use of this algorithm leads to a considerable reduction in disk space and timing. © 1994 by John Wiley & Sons, Inc.     

Spin catalysis: dynamics of three-spin systems

The kinetic theory of a new phenomenon, spin catalysis, has been developed. This phenomenon takes place in three-spin systems, when the third radical (or a paramagnetic ion) induces spin conversion in the pair, removes spin forbiddance, and thus changes the reactivity of the first two radicals. Kinetic equations for yields of spin catalyzed reactions have been derived. Conditions for spin catalysis, values of the catalytic effect, and the kinetic behavior are discussed. A new kind of quantum beats in chemical reactions is predicted.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 9, pp. 1646–1652, September, 1995.This work was financially supported by the Russian Foundation for Basic Research (Project No. 93-03-05227).     

Isomeric interconversion in the linear Cl(-)-HD anion complex

The rotationally resolved infrared photodissociation spectrum of Cl(-)-HD is measured in the HD stretch region. Two Sigma-Sigma bands are observed, corresponding to transitions from the ground state [the (nuHD = 0, n = 0) level] and first excited intermolecular bend state [the (nuHD = 0, n = 1) level]. The (nuHD = 0, n = 0) and (nuHD = 0, n = 1) states are predominantly associated with the linear Cl-...DH and Cl-...HD geometries, respectively. The spectrum is complicated by perturbative interactions between levels of the (nuHD = 0, n = 0) and (nuHD = 0, n = 1) rotational manifolds and between levels of the (nuHD = 1, n = 0) and (nuHD = 1, n = 1) rotational manifolds. A global fit to the transition frequencies, taking the lower and upper state perturbations into account, yields zero-order rotational and centrifugal distortion constants and allows us to establish that the (nuHD = 0, n = 1, J" = 0) level lies 13.7 cm(-1) above the (nuHD = 0, n = 0, J" = 0) level. Rovibrational energy level calculations performed using a recent ab initio potential energy surface confirm the picture emerging from the experimental data and provide good agreement with measured molecular parameters. The results emphasize the importance of quantum mechanical interconversion between two isomeric structures of a simple anion complex.     

Photoelectron spectroscopy of the Cl(-)...H(2)D(2) anions: a model beyond the rotationless and Franck-Condon approximations

A model for simulating photoelectron spectra of the triatomic van der Waals complexes containing stable atomic anion and diatomic molecule is proposed and applied to the Cl(-)...H(2) and Cl(-)...D(2) anions. The model assumes adiabatic separation of the electronic and nuclear motions and localization of the photodetachment act at the atomic chromophore. Under these approximations, the electronic transition dipole moment matrix elements are evaluated using the atoms-in-molecule approach and explicit expressions for the rovibrational line strength factors are derived. The energies and intensities of a number of rovibronic photoelectron transitions are calculated for the Cl(-)...H(2) and Cl(-)...D(2) anions within the adiabatic bender model, i.e., with the full separation of the vibrational motions, whereas the simulations of the broad spectral envelopes are performed using the equilibrium conditions, asymmetric line shape function, and two choices of the relative abundances of the para- and ortho-forms of the complex. The simulations reproduce experimental spectra reasonably well allowing for their unambiguous assignment in terms of vibronic transitions fully consistent with the previous time-dependent calculations. Agreement with the previous theoretical works, manifestations of non-Franck-Condon effects, and implications to the assessment of the neutral potential energy surfaces are discussed.