[en] To reduce the dimension of a vibrational problem to be solved by the coupled channel method in the case of interacting electronic states of diatomic molecules, we propose to use the contact van Vleck transformations, which make it possible to take into account the nonadiabatic intramolecular interactions with distant states by modifying the initial potential energy matrix. The efficiency of the reduced coupled vibrational channel method (RCVCM) has been demonstrated by an example of analyzing the regular spin–orbital, electron–rotational, and spin–rotational perturbations discovered in the fine structure of vibrational–rotational levels of the $c^3{\mathrm{\Sigma <!--\; ??\; -->}}_{\mathrm{\Omega <!--\; ??\; -->}}^{+}$-state of a KRb molecule by methods of high-precision laser-emission spectroscopy. The adiabatic potentials and nonadiabatic electron matrix elements, as functions of the internuclear distance necessary for application of the RCVCM, were obtained in the framework of the nonempirical high-level calculation. It has been demonstrated that the RCVCM has broad extrapolation possibilities and makes it possible to describe the position of the regularly perturbed energy levels of Ω-components of the triplet $c^3{\mathrm{\Sigma <!--\; ??\; -->}}_{\mathrm{\Omega <!--\; ??\; -->}}^{+}$‑state at the spectroscopic accuracy level.

No abstract available

[en] Numerical simulation of the effect of intramolecular electrostatic interactions on redistribution of relative intensities in the vibrational structure of (1 ~ 2)¹Π–X¹Σ⁺ rotationally resolved transitions of the KRb molecule is performed within the precision nonadiabatic model of coupled vibrational channels. It is established that mutual perturbation of electronically excited states modifies in a nontrivial way a nodal structure of nonadiabatic wavefunction of the (1 ~ 2)¹Π complex, which is possible to use for rising efficiency of twostep laser synthesis and stabilization of ultracold ensembles of KRb molecules in the ground electronic state.

No abstract available

[en] Modern molecular spectroscopy of diatomic molecules is the precision study of the structure and dynamics of electronically excited states of isolated molecules in the gas phase. At the same time, the energy, radiation, magnetic, and electrical characteristics of excited molecules, which are of interest for different physicochemical applications, must be determined and predicted at the experimental (spectral) level of accuracy in a broad range of electron vibrational and rotational excitations. This problem cannot be solved within spectroscopy’s traditional adiabatic approximation, since a large number of intramolecular interactions (so-called perturbations) inevitably distorts not only the regular energy structure of different levels but he nodal structure of the corresponding wave functions as well. The most accurate solution to both direct and inverse spectroscopic problems with respect to perturbed molecular states is based on constructing a reduced system of the coupled radial Schrödinger equations encountered in the quantum-mechanical modeling of the nonadiabatic interaction of electronic states. The nonadiabatic approach can be employed successfully only through the joint use of precision spectroscopic data and highly precise calculations of electronic structure.

[en] The pair interaction potentials of the weakly bound Rb–CH₄ and Cs–CH₄ systems, which are active media of alkali metal vapor lasers with broadband diode or excimer laser pumping, were calculated by the ab initio method. The electronic problem was solved by the coupled-cluster method in the CCSD(T) version including the basis set superposition error and extrapolation to an infinite basis set. The obtained pointwise ab initio potentials were approximated by the analytical functions based on the orthogonal Chebyshev polynomial expansion with correct asymptotic behavior at the dissociation limit and then used within the framework of the molecular kinetic theory of rarefied gases to evaluate the reduced collision integrals and mutual diffusion coefficients.

[en] The review concerns the potential of modern high-resolution laser spectroscopy and state-of-the-art ab initio electronic structure calculations used to obtain comprehensive information on the energy and radiative properties of strongly coupled rovibronic diatomic states. The possibility of deperturbation treatment of the intermediate electronically excited states at the experimental (spectroscopic) level of accuracy is demonstrated taking alkali metal dimers as examples. The deperturbation analysis is of crucial importance to optimize multistep laser synthesis and stabilization of ultracold molecular ensembles in their absolute ground level. The bibliography includes 227 references

[en] Using high-precision nonempirical methods of modern quantum chemistry, the effect of the weak relativistic interactions on the potential energy and the permanent dipole moment of the ground electronic state of the CO molecule is studied. The relativistic energy is calculated by the following three optional methods: within the first-order perturbation theory using the Cowan–Griffin operator containing the sum of the mass-velocity and Darwin corrections, within the framework of the approximate Douglas–Kroll–Hess scalar Hamiltonian, and the most rigid “four-component” relativistic Dirac–Coulomb–Gaunt Hamiltonian. The relativistic correction obtained by different methods agrees within a few percents and equals about 55–60 cm^–1 in the region of an equilibrium internuclear distance of $R_e=1.128$ Å. The addition of the relativistic correction decreases the equilibrium bond length by about 0.0002 Å. The magnitude of the Lamb shift estimated by the semiempirical scaling of the one-electron Darwin’s term does not exceed several inverse centimeters near $R_e$. The relativistic correction to the dipole moment function is in the range from –0.001 to +0.003 D, which does not exceed 1% of the nonrelativistic component of the dipole moment.

[en] The results of laboratory mass-spectrometer studies of the laser-induced dissociation of molecules of simple aromatic hydrocarbons adsorbed on a quartz substrate under the conditions of deep vacuum and low temperatures are adapted to the physical and chemical conditions in regions of active star formation in molecular clouds. The main properties of the photolysis of physically adsorbed molecules compared to the photodissociation of isolated molecules in the gas phase are identified. The relevance of molecular photolytic desorption to the real conditions in the interstellar medium is analyzed, in particular, to the conditions in photodissociation regions. It is shown that the photodissociation of adsorbed benzene occurs along other channels and with appreciably lower efficiency than does the corresponding process in the gas phase. The photodissociation of aromatic hydrocarbons adsorbed on the surfaces of interstellar grains cannot make a large contribution to the abundance of hydrocarbons with small numbers of atoms observed in the interstellar medium.

[en] The laser-induced fluorescence (LIF) A ¹Σ⁺-b ³Π→X ¹Σ⁺ spectra of the KCs molecule were recorded in a near infrared region by a Fourier-transform spectrometer with a resolution of 0.03 cm^-1. Overall more than 200 collisionally enhanced LIF spectra were rotationally assigned to ³⁹K¹³³Cs and ⁴¹K¹³³Cs isotopomers yielding more than 3400 rovibronic term values of the strongly mixed singlet A ¹Σ⁺ and triplet b ³Π states with the uncertainty of 0.003-0.01 cm^-1. Experimental data massive starts from the lowest vibrational level v_A=0 of the singlet and nonuniformly covers the energy range E is an element of [10 040,13 250] cm^-1 with rotational quantum numbers J^' is an element of [7,225]. Besides the dominating regular A ¹Σ⁺-b ³Π_Ω=0 interactions, the weak local heterogeneous A ¹Σ⁺-b ³Π_Ω=1 perturbations have been discovered and analyzed. Coupled-channels deperturbation analysis of the experimental ³⁹K¹³³Cs e-parity term values of the A ¹Σ⁺-b ³Π_Ω=0,1,2 complex was accomplished in the framework of the phenomenological 4x4 Hamiltonian accounting implicitly for regular interactions with the remote ¹Π and ³Σ⁺ states. The diabatic potential energy curves of the A ¹Σ⁺ and b ³Π states, as well as relevant spin-orbit coupling matrix elements, were defined analytically with the expanded Morse oscillators model. The obtained parameters reproduce 95% of experimental data field of the ³⁹K¹³³Cs isotopomer with a standard deviation of 0.004 cm^-1, which is consistent with the uncertainty of the experiment. Reliability of the derived parameters was confirmed by a good agreement between the predicted and experimental term values of the ⁴¹K¹³³Cs isotopomer. The calculated relative intensity distributions in A-b→X LIF progressions are also consistent with their experimental counterparts. The deperturbation model was applied for simulation of a pump-dump optical cycle a ³Σ⁺→A ¹Σ⁺-b ³Π→X ¹Σ⁺ proposed for transformation of ultracold KCs molecules to their absolute ground state v_X=0;J_X=0.