Cyclization versus oligomerization of SP- and RP-5′-OH-N-benzoyl-2′-deoxycytidine-3′-O-(2-thio-4,4-pentamethylene-1,3,2-oxathiaphospholane)s

The S_P-isomer of 5′-OH-N⁴-benzoyl-2′-deoxycytidine-3′-O-(2-thio-4,4-pentamethylene-1,3,2-oxathiaphospholane) undergoes DBU-promoted intramolecular cyclization providing as a sole product S_P-deoxycytidine cyclic 3′,5′-O,O-phosphorothioate. Unexpectedly, the R_P-counterpart yields a mixture of products consisting of R_P-deoxycytidine cyclic 3′,5′-O,O-phosphorothioate and macrocyclic oligo(deoxycytidine phosphorothioate)s. The results of molecular modeling indicate that the dychotomy observed for the R_P substrate may result from remarkably higher energy of the corresponding transition states, caused by the presence of bulky ‘spiro’ pentamethylene substituent at the position C4 in the oxathiaphospholane ring.     

Harmonic oscillators in relativistic quantum mechanics

Relativistic generalisations of the harmonic oscillator are analysed. Lévy–Leblond, Dirac and Klein–Gordon equations which in the limit of a non-relativistic and spinless particle transform into Schrödinger equation for the harmonic oscillator are constructed. Properties of their solutions, in particular the structure of their spectra, are analysed. Applications to modelling phenomena relevant in quantum chemistry are briefly discussed.     

Statistical properties of spin-adapted reduced Hamiltonians

The first two moments of the spectral density distributions of the second- and the third-order spin-adapted reduced Hamiltonian (SRH ) matrices have been calculated and compared with the corresponding quantities describing the full configuration interaction (FCI ) Hamiltonian matrix. It has been demonstrated that the differences between the SRH and FCI spectral density distributions sharply increase with increasing difference between the number of electrons and the order of SRH . © 1994 John Wiley & Sons, Inc.     

Relativistic and correlation corrections to electron affinities of alkali and halogen atoms

Electron affinities (EAs) of alkali and halogen atoms have been calculated using Hartree-Fock and Dirac-Hartree-Fock methods. Comparing the results with the experimental values, relativistic and correlation corrections to EAs have been estimated. In the case of alkalines correlation correction constitute 110%–120% of the experimental EA values. In the case of halogens the corresponding numbers are 30%–60%. Relativistic effects are negligibly small for alkalines but significant for halogens (40% of the experimental value for At).     

Characters of two-row representations of the symmetric group

Characters of irreducible representations (irreps) of the symmetric group corresponding to the two-row Young diagrams, i.e., describing transformation properties of N-electron eigenfunctions of the total spin operators, have been expressed as explicit functions of the number of electrons N and of the total spin quantum number S. The formulas are useful in various areas of theory of many-electron systems, particularly in designing algorithms for evaluation of spectral density moments. © 1997 John Wiley & Sons, Inc.     

On the anisotropy of multi-chance, high-spin fission

Inclusion of the fission-fragment anisotropy in statistical-model analyses is shown to provide significant constraints on the spin and chance distributions for high-spin fission. Selective anisotropy measurements which should enhance sensitivity to shell or pairing corrections in the late stages of compound-nucleus decay are suggested.     

Investigation of polar emission in 252Cf and 235U + nth fission

The energy distributions and relative intensities of protons, deuterons, tritons and α-particles emitted along the fission axis during spontaneous fission of ²⁵²Cf were measured simultaneously with both fission fragment energies. The absolute intensity of particles, the mass distribution of fragments, the total kinetic energy and total excitation energy of both fragments were subsequently deduced from the experimental data. Statistical model calculations based on a hypothesis that the polar particles are evaporated from fission fragments have been performed for ²⁵²Cf and ²³⁶U fission. Although some experimental results agree remarkably well with the evaporation hypothesis, the considered model cannot describe many features of the polar emission phenomenon.     

On the symmetrized cones in test function algebra

The cones K and C in the algebra of test functions involved in the notions of positivity and T-positivity are studied. We prove that the closures of symmetrized cones sK, sC and sK + sC are proper cones.