ИСТИНА

Modern laser technologies make it possible to synthesize stable ensembles of atoms and molecules at ultralow temperature. Ultracold molecular gases can serve as an ideal medium in the search for an electron’s permanent dipole moment, in the creation of new time and frequency standards, in study of a possible change in fundamental physical constants on a cosmological time scale, and in controlling the mechanism of a chemical reaction by an external magnetic and/or electric field. Nowadays methods of laser synthesis of ultracold molecular ensembles are based on photoassociation or magnetoassociation of individual atoms, previously storaged in magneto-optical traps. To optimize the laser "assembly" of molecules from ultracold atoms, we need highly accurate data on the structure and dynamics of weakly bound atomic pairs. Thus, for effective modeling of multistep optical cycles of laser synthesis of ultracold molecules, it is necessary to know the energies and radiative properties of rovibronic states localized near the dissociation limit of the corresponding molecule at an unprecedented level of accuracy. In the case of alkali metal dimers, this quantum-mechanical model should certainly consider hyperfine and spin-spin interactions between electron states converging to the same threshold dissociation. From the analysis of the position and width of the observed Feshbach resonances unambiguously established that intramolecular "mixing" of quasidegenerate levels of the singlet and triplet states of alkali dimers results in a drastic change in the position and transition probabilities to hyperfine components of X1Σ+~ a3Σ+ complex. In this report, we simulate the effect of hyperfine and spin-spin interaction on the rovibronic structure of the KCs molecule near the ground dissociation threshold using (1) on nonempirical relativistic calculations of the hyperfine structure parameters as a function of the internuclear distance, (2) taking into account the fine and hyperfine mixing of the singlet and triplet states in the framework of the coupled channel model, and (3) on the refinement of the obtained estimates by comparing them with the precise experimental data on the line position and intensities of laser-induced fluorescence spectra on the X1Σ+~ a3Σ+ complex.