Coherent chemistry and biochemistry

The paprer presents analysis of coherent process in chemistry at all its level. Electronic, vibrational, electron-spin, nuclear-spin, and macroscopic coherencies are considered; physical backgrounds of coherent phenomena as well as their chemical consequences are also discussed.     

Interactions between anionic and neutral bromine and rare gas atoms

High-quality, ab initio potential energy functions are obtained for the interaction of bromine atoms and anions with atoms of the six rare gases (Rg) from He to Rn. The potentials of the nonrelativistic (2)Sigma(+) and (2)Pi electronic states arising from the ground-state Br((2)P)-Rg interactions are computed over a wide range of internuclear separations using a spin-restricted version of the coupled cluster method with single and double excitations and noniterative correction to triple excitations [RCCSD(T)] with an extrapolation to the complete basis set limit, from basis sets of d-aug-cc-pVQZ and d-aug-cc-pV5Z quality. These are compared with potentials derived previously from experimental measurements and ab initio calculations. The same approach is used also to refine the potentials of the Br(-)-Rg anions obtained previously [Buchachenko et al., J. Chem. Phys. 125, 064305 (2006)]. Spin-orbit coupling in the neutral species is included both ab initio and via an atomic approximation; deviations between two approaches that are large enough to affect the results significantly are observed only in the Br-Xe and Br-Rn systems. The resulting relativistic potentials are used to compute anion zero electron kinetic energy photoelectron spectra, differential scattering cross sections, and the transport coefficients of trace amounts of both anionic and neutral bromine in the rare gases. Comparison with available experimental data for all systems considered proves a very high precision of the present potentials.     

Quantum-chemical study of endohedral fullerenes

State-of-the-art in quantum-chemical research on endohedral fullerenes is considered. Separate chapters are devoted to complexes with noble gases, main group elements, and methals and their nitrides. The structures and the mechanisms of formation and decomposition of these compound sare highlighted. Applicability of various quantum-chemical methods for endohedral fullerene complexes is discussed. Problems associated with the use of the ROHF and UHF methods are revealed. The DFT method with hybrid functionals and effective core potentials for heavy atoms is shown to hold the greatest promise.     

Photochemical reactions of 9-trimethylstannylanthracene in various solvents

9-Trimethylstannylanthracene (1) was synthesized and its photolysis by 365-nm light was studied. In aprotic solvents, the dimerization of 1 involves positions 9 and 10 and yields a head-to-tail dimer. The main route of the photolysis of 1 in alcohols is the cleavage of the C-Sn bond with the formation of anthracene. The quantum yields of the photoreaction and the lifetimes and quantum yields of 1 fluorescence were determined.     

Interactions of 2P atoms with closed-shell diatomic molecules: alternative diabatic representations for the electronic anisotropy

The matrices of electrostatic and spin-orbit Hamiltonians for the system of a 2P atom interacting with a closed shell diatomic molecule in uncoupled, coupled, and complex-valued representations for electronic diabatic basis functions are rederived, and the unitary transformations connecting them are given explicitly. The links to previous derivations are established and existing inconsistencies are identified and eliminated. It is proven that the block-diagonalization of a 6 x 6 matrix of the electronic Hamiltonian is a result of using the basis functions with well-defined properties with respect to time reversal. Consideration of time-reversal symmetry also enforces phase consistency relevant for applications to multisurface reactive scattering and photodetachment spectroscopy calculations, as well as for perspective studies of inelastic effects in cold and ultracold environments. These and further developments are briefly sketched.     

van der Waals interactions and dipole polarizabilities of lanthanides: Tm(2F)-He and Yb(1S)-He potentials

Anisotropic dipole polarizabilities of Tm(2F), Tm+2(2F), and Yb(1S) are calculated using the finite-field multireference averaged quadratic coupled cluster (MR-AQCC) (Tm and Tm+2) and RCCSD(T) (Yb) methods with small-core relativistic pseudopotentials ECP28MWB combined with the augmented ANO basis sets. The lanthanide atoms are strongly polarizable with the scalar part originating from the 6s electrons and the tensorial part from the open 4f shells. The adiabatic interaction potentials 2Sigma+, 2Pi, 2Delta, and 2Phi of Tm(2F)-He and Tm+2(2F)-He were examined by the multireference approaches, multireference configuration interaction and MR-AQCC, using the basis sets designed in the polarizability calculations. A closed-shell lanthanide system Yb(1S)-He was included for comparison. The Tm-He 2Sigma+, 2Pi, 2Delta, and 2Phi interaction potentials are very shallow and nearly degenerate (within 0.01 cm(-1)), with the well depths in the range of 2.35-2.36 cm(-1) at R=6.17 A. The basis-set saturated well depths are expected to be larger by ca. 25%, as estimated using the bond-function augmented basis set. The interactions of lanthanide atoms with He are one order of magnitude less anisotropic than those involving first-row transition metal atoms. The suppression of anisotropy is chiefly attributed to the screening effected by the 6s shell. When these electrons are removed as in the di-cation complex Tm+2(2F)-He, the potentials deepen to a thousand wave number range and their anisotropy is enhanced 500-fold.     

Interaction potentials for Br(-)-Rg (Rg=He-Rn): spectroscopy and transport coefficients

High-level ab initio CCSD(T) calculations are performed in order to obtain accurate interaction potentials for the Br(-) anion interacting with each rare gas (Rg) atom. For the Rg atoms from He to Ar, two approaches are taken. The first one implements a relativistic core potential and an aug-cc-pVQZ basis set for bromine, an aug-cc-pV5Z basis set for Rg, and a set of bond functions placed at the midpoint of the Rg-Br distance. The second one uses the all-electron approximation with aug-cc-pV5Z bases further augmented by an extra diffuse function in each shell. Comparison reveals close similarity between both sets of results, so for Rg atoms from Kr to Rn only the second approach is exploited. Calculated potentials are assessed against the previous empirical, semiempirical, and ab initio potentials, and against available beam scattering data, zero electron kinetic energy spectroscopic data, and various sets of the measured ion mobilities and diffusion coefficients. This multiproperty analysis leads to the conclusion that the present potentials are consistently good for the whole series of Br(-)-Rg pairs over the whole range of internuclear distances covered.     

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