arXiv subjects

A. B. Alekseyev

Publications and source records attributed to A. B. Alekseyev.

3 recordsLinked to original sources

arXiv2014

Photodissociation of interstellar ArH+

Aims. Following the recent detection of 36ArH+ in the Crab nebula spectrum, we have computed the photodissociation rate of ArH+ in order to constrain the physical processes at work in this environment. Methods. Photodissociation cross sections of ArH+ are computed in an ab initio approach including explicit account of spin-orbit coupling. Results. We report the photodissociation cross section of ArH+ as a function of wavelength. Photodissociation probabilities are derived for different impinging radiation fields.The photodissociation probability of for a very small unshielded cloud surrounded on all sides by the unshielded InterStellar Radiation Field (ISRF) model described by Draine (1978) is equal to 9.9e-12 s-1 and 1.9e-9 s-1 in the Crab nebula conditions. The dependence on the visual extinction is obtained by using the Meudon Photon Dominated Region (PDR) code and corresponding analytical fits are provided. Conclusions. These data will help to produce a realistic chemical network to interpret the observations. Photodissociation of ArH+ is found to be moderate and the presence of this molecular ion is mainly dependent on the molecular fraction

astro-ph.GA↗

arXiv2001

GRECP/5e-MRD-CI calculation of the electronic structure of PbH

The correlation calculation of the electronic structure of PbH is carried out with the Generalized Relativistic Effective Core Potential (GRECP) and MultiReference single- and Double-excitation Configuration Interaction (MRD-CI) methods. The 22-electron GRECP for Pb is used and the outer core 5s, 5p and 5d pseudospinors are frozen using the level-shift technique, so only five external electrons of PbH are correlated. A new configuration selection scheme with respect to the relativistic multireference states is employed in the framework of the MRD-CI method. The [6,4,3,2] correlation spin-orbit basis set is optimized in the coupled cluster calculations on the Pb atom using a recently proposed procedure, in which functions in the spin-orbital basis set are generated from calculations of different ionic states of the Pb atom and those functions are considered optimal which provide the stationary point for some energy functional. Spectroscopic constants for the two lowest-lying electronic states of PbH ($^2Π_{1/2}, ^2Π_{3/2}$) are found to be in good agreement with the experimental data.

physics.chem-ph↗

arXiv2000

GRECP/MRD-CI calculations of the spin-orbit splitting in the ground state of Tl and of the spectroscopic properties of TlH

The generalized relativistic effective core potential (GRECP) approach is employed in the framework of multireference single- and double-excitation configuration interaction (MRD-CI) method to calculate the spin-orbit (SO) splitting in the $^2P^o$ ground state of the Tl atom and spectroscopic constants for the $0^+$ ground state of TlH. The 21-electron GRECP for Tl is used and the outer core 5s and 5p pseudospinors are frozen with the help of the level shift technique. The spin-orbit selection scheme with respect to relativistic multireference states and the corresponding code are developed and applied in the calculations. In this procedure both correlation and spin-orbit interactions are taken into account. A [4,4,4,3,2] basis set is optimized for the Tl atom and employed in the TlH calculations. Very good agreement is found for the equilibrium distance, vibrational frequency, and dissociation energy of the TlH ground state ($R_e=1.870 Å, ω_e=1420 cm^{-1}, D_e=2.049 eV$) as compared with the experimental data ($R_e=1.868 Å, ω_e=1391 cm^{-1}, D_e=2.06 eV$).

physics.chem-ph↗