On quark molecules

The nonrelativistic quark model with three triplets and an octet of coloured gluons is examined. The interaction energy corresponding to certain quark molecules is calculated. It is shown that systems of $\text{qq}\text{qq}$ and $\text{qqqq}\text{q}$ are more strongly bound than $\text{q}\text{q}$ and qqq. Thus in order for the model to be valid there must exist exotic particles.     

On some generalizations of the Weinberg model

A generalization of the Weinberg model of leptons is proposed which introduces additional gauge fields. Experimental consequences for the amplitude of νe scattering the W-boson masses are discussed.     

Band filling and interband scattering effects in MgB2: carbon versus aluminum doping

We argue, based on band structure calculations and the Eliashberg theory, that the observed decrease of T(c) of Al and C doped MgB2 samples can be understood mainly in terms of a band filling effect due to the electron doping by Al and C. A simple scaling of the electron-phonon coupling constant lambda by the variation of the density of states as a function of electron doping is sufficient to capture the experimentally observed behavior. Further, we also explain the long standing open question of the experimental observation of a nearly constant pi gap as a function of doping by a compensation of the effect of band filling and interband scattering. Both effects together generate a nearly constant pi gap and shift the merging point of both gaps to higher doping concentrations, resolving the discrepancy between experiment and theoretical predictions based on interband scattering only.     

Model of interband pairing in mixed valence and heavy fermion systems

Various possible types of interband pairings in mixed valence and heavy fermion systems are investigated, using a two-band model with Kondo-type interaction. In this model, the system may develop interband singlet superconducting ordering, or electron-hole pairing of excitonic type, which induces an effectivef – d hybridization. The conditions for the realization of each of these orderings depends crucially on the dispersion of the corresponding original bands. The mutual influence of the two pairings, as well as the effect of external hybridization, are investigated.     

Theoretical study of the structure of the CClF2NO and CCl2FNO molecules in the ground and lowest excited singlet and triplet electronic states

The potential energy surfaces of the nitroso compounds CClF₂NO and CCl₂FNO in the ground and lowest excited singlet and triplet electronic states were studied by various ab initio methods (including multiconfigurational methods). The equilibrium geometric parameters, vibrational frequencies, internal rotation potential functions, and rotational contours of bands in the S₁ S₀ vibronic spectrum of the CClF₂NO molecule were calculated. For the molecules under consideration, the quantum-mechanical problem on torsional motion was solved. The results of calculations are, on the whole, in good agreement with experiment.     

Relaxation, self-trapping, and decay of electron excitations in wide-gap oxides

Emission spectra ofMgO, Al ₂O₃, Y₂O₃, andSc ₂O₃ crystals, excited at 8 K by photons with energies 5–40 eV, are measured. The luminescence of free excitons andGe ²⁺ centers forMgO, the self-trapped exciton emission (STEE) forAl ₂O₃ andY ₂O₃, and the tunnel self-luminescence forScO ₃ are studied. A distinction between hole polarons in oxides and self-trapped holes in halides leads to a sharp difference in the mechanisms of STEE creation on electronhole recombination for these two classes of solids. The electron-hole, hole-electron, and exciton mechanisms of excitation multiplication are identified. The high radioresistance of wide-gap oxides and the behavior of oxygen interstitials inMgO crystals are discussed. Institute of Physics of Estonia. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 3, pp. 5–16, March, 2000.