Photochemical reactions of organomercury compounds in organic solvents

The quantum yields of photolysis of organomercury compounds in different organic solvents have been measured. It was shown that the quantum yields of photolysis of nitro derivatives of mercury compounds and the symmetric (methylnaphtyl)mercury compound are equal to unity. The photolysis of halo derivatives of benzylmercury proceeds with lower quantum yields as compared with photolysis of analogous dibenzylmercury derivatives. The quantum yields of photolysis of organomercury compounds are almost independent of the solvent.     

Modeling of catalytic activity of an Al2O3 surface on the basis of the first principles

The adsorption, desorption, impact, and associative heterogeneous recombination rate coefficients are determined for atomic oxygen in the temperature range between 500 and 2000 K on the basis of quantum chemical data on the energy of interaction of atomic and molecular oxygen with the clusters that model an α-Al₂0₃ surface. These coefficients are used to calculate the heterogeneous recombination probabilities and the heat fluxes to the surface under the conditions similar to those of the MESOX facility.     

Oriented dynamics in van der Waals complexes

The effects of relative orientation on collision and reaction dynamics can be examined by characterizing the unimolecular decay of van der Waals complexes. Most commonly, decomposition is initiated by exciting one of the monomers within a complex, and the relative orientation is defined by the zero-point motions for the intermolecular degrees of freedom. However, if simultaneous excitation of the intermolecular degrees of freedom is achieved, a considerable range of starting configurations may be accessed. We are currently studying I₂-Rg and CN-H₂/D₂ complexes with the goal of using these systems to examine oriented dynamics. For I₂(B)-Ne we have observed excited intermolecular vibrations and the effects of these motions on the predissociation dynamics. The correlation between structure and dynamics suggested by these results can be understood using classical mechanics, but the implications of this model are at variance with accepted ideas about the topology of I₂(B)-Rg potential surfaces. Spectroscopic and theoretical studies of CN-H₂/D₂ indicate that this pre-reactive complex may be used to examine steric effects in the H₂+CN→H+HCN reaction. The complex was characterized using the A-X and B-X electronic transitions. As is often the case for weakly bound systems, the insights provided by high-level theoretical calculations were essential for interpretation of the spectra. The properties of excited intermolecular vibrations of CN-H₂ were predicted as a prelude to studies of the intra-cluster reaction dynamics.     

Intensities of the photoelectron spectra of weakly bound anions: A complex of an atomic anion with a diatomic molecule

A closed formula for the state-resolved photodetachment probabilities of an electron from a weakly bound complex of an atomic anion with a diatomic molecule residing in a nondegenerate electronic state is obtained. Due to the reduction of the dipole moment matrix elements in terms of molecular electronic wave functions to the matrix elements in terms of atomic wave functions, the formula allows one to calculate the relative intensities of the photoelectron spectrum taking into account rovibrational and spin-orbit interactions and using practically convenient representations of the wave functions of the bound initial state of an anionic complex and of the bound or unbound final state of a neutral system. The methods of estimation of the atomic dipole moment matrix elements, the error due to neglect of the photoelectron rescattering, and possible modifications and generalizations of the formula are discussed.     

Modeling the H5+ potential-energy surface: a first attempt

 Ab initio molecular electronic structure calculations are performed for H₅ ⁺ at the QCISD(T) level of theory, using a correlation-consistent quadruple-zeta basis set. Structures, vibrational frequencies and thermochemical properties are evaluated for ten stationary points of the H₅ ⁺ hypersurface and are compared with previous calculations. The features of the H₃ ⁺…H₂ interaction at intermediate and large intermolecular distances are also investigated. Furthermore, an analytical functional form for the potential-energy surface of H₅ ⁺ is derived using a first-order diatomics-in-molecule perturbation theory approach. Its topology is found to be qualitatively correct for the short-range interaction region. Received: 15 March 2001 / Accepted: 5 July 2001 / Published online: 11 October 2001     

The n.m.r. of paramagnetic complexes of vanadyl acetylacetonate with organic phosphites and hydroperoxides

The vanadium IV ion in vanadyl acetylacetonate (V^IV) forms labile paramagnetic complexes with organic phosphites in the first coordination sphere. The enthalpy of complex formation between V^IV and triphenyl phosphite was 2.6 kcal mol^?1. Complex formation enthalpies ΔH and the activation energies E of ligand (hydroperoxide) escape from the metal ion sphere were determined from the temperature dependence of paramagnetic broadening of the n.m.r. lines of hydroperoxides in the presence of vanadyl acetylacetonate. At low temperatures the phosphite sharply weakens the bond between the metal ion and hydroperoxide in the second coordination sphere (ΔH decreases fivefold). Taken in excess, phosphite displaces the hydroperoxide molecules from the coordination sphere of the V^IV ion and thus blocks it. The observed n.m.r. characteristics of the paramagnetic complexes explain, on the model level, the kinetic regularities of the reaction of hydroperoxides with phosphite catalysed by transient metal ions.     

Inducing Dynamic Nuclear Polarization in Chemical Reactions

The experimental studies of the dynamic nuclear polarization In the chemical reactions(CINDP)[1-11] discover some characteristic peculiarities — the unusual behaviour of the spin multiplets, the appearance of nuclear polarization in the products of cage radical recombination, and finally, the dependence of the sign of polarization upon the type of reaction in which the radical participates. These pecularities are specific for CINDP and differentiate CINDP from the ordinary two-frequency dynamic nuclear polarization.