V. E. Chernov

Dynamic polarizabilities of atoms in their low-excited states : He, Be, Mg and Ca

The quantum defect Green function formalism is applied to calculate the dynamic scalar and tensor polarizabilities of some atoms in their excited states (21S, 23S, 21P and 23P for He, 21P and 23P for Be, 33P for Mg and 43P for Ca). Experimental and calculated oscillator strength values were used to provide an account for low-excited states (reduce–adding correction of the Green function) while the high-excited and continuum states are accounted semi-analytically. The calculated polarizability values are in good (within several per cent) agreement with the available experimental data and the ab initio numerical data.

Time-resolved FTIR emission spectroscopy of Cu in the 1800{3800 cm -1 region: Transitions involving f and g states and oscillator strengths

Time-resolved Fourier-transform spectroscopy was applied to the study of the emission spectra of Cu vapours in a vacuum (10−2 Torr) produced in ablation of a Cu metal target by a high-repetition rate (1.0 kHz) pulsed nanosecond ArF laser (λ = 193 nm, output energy of 15 mJ). The time-resolved infrared emission spectrum of Cu was recorded in the 1800–3800 cm−1 spectral region with a resolution of 0.017 cm−1. The time profiles of the measured lines have maxima at 18–20 µs after a laser shot and display non-exponential decay with a decay time of 5–15 µs. This study reports 17 lines (uncertainty 0.0003–0.018 cm−1) of Cu I not previously observed. This results in seven newly-found levels and revised energy values for 11 known levels (uncertainty 0.01–0.03 cm−1). We also calculate transition probabilities and oscillator strengths for several transitions involving the reported Cu levels.

Diabatic Rydberg states in polar molecules with a complex core

Based on a new solution of the Schrodinger equation for an electron in Coulomb + rotating dipole potential, diabatic (inverse Born-Oppenheimer) Rydberg states are treated in polar molecules. The obtained exact solution contains explicit dependence on the molecular core coupling scheme which is considered to be intermediate between Hunds (a), (c) and (b) cases. Analytical expressions are derived for the diabatic quantum defects of the Rydberg states in polar molecules with such a complex core.

Pseudopotential calculations of photoionization of atoms in the x-ray photon energy range and FEL beam monitor development

A pseudopotential model for calculation of atomic processes under interaction with hard x-ray photons is applied to calculation of Krypton photoionization cross sections?by photons with energy in the 20?25?keV range. These cross sections, as well as the mean charge of the resulting ions calculated using the Monte Carlo simulation scheme, are in good agreement with the other theoretical calculations and with the experiment. The obtained results open the doors for new techniques in the design of gas-monitor detectors to control the intensity, coordinates and energy of x-ray free-electron laser (XFEL) beams in the hard x-ray photon energy range. First, Monte Carlo simulations of a scintillation detector application for gas-monitors have been performed.

Polarizability of the fine-structure components of low excited states of-the F, Cl, and Br atoms

The dynamic scalar, tensor, and pseudovector polarizabilities of the low excited states (ns)4PJ of the F, Cl, and Br atoms (n = 3, 4, and 5, respectively) are calculated for all the levels of the fine-structure multiplets with J = 5/2, 3/2, and 1/2 with the use of the quantum detect Green’s function, proposed earlier.

Method of the quantum defect Green's function for calculation of dynamic atomic polarizabilities

The quantum defect Green’s function enabling one to take into account exactly the contribution of highly excited and continuum states to the polarizability is found. The contribution of the ground and low-lying excited states is taken into account by using experimental values of the corresponding oscillator strengths. The good accuracy of the method proposed is demonstrated by calculation of the scalar dipole dynamic polarizabilities of noble gas atoms with consideration of the fine structure of the terms.

Chaotic diffusion on periodic orbits: The perturbed Arnold cat map

Chaotic diffusion on periodic orbits (POs) is studied for the perturbed Arnold cat map on a cylinder, in a range of perturbation parameters corresponding to an extended structural-stability regime of the system on the torus. The diffusion coefficient is calculated, using the following PO formulas: (1). the curvature expansion of the Ruelle zeta function; (2). the average of the PO winding-number squared, w(2), weighted by a stability factor; (3). the uniform (nonweighted) average of w(2). The results from formulas (1). and (2). agree very well with those obtained by standard methods, for all the perturbation parameters considered. Formula (3). gives reasonably accurate results for sufficiently small parameters corresponding also to cases of a considerably nonuniform hyperbolicity. This is due to uniformity sum rules satisfied by the PO Lyapunov eigenvalues at fixed w. These sum rules follow from general arguments and are supported by much numerical evidence.

Rotational Rydberg States of Polar Molecules: Hund's Classification and Zeeman Effect

The rotational Rydberg states of polar molecules, which arise as a result of the interaction of a Rydberg electron with core rotations, are considered. A large number of angular momenta in the core-electron system lead to a considerably greater number of possible coupling schemes of these momenta compared to the number of schemes determined by the classical five Hund’s cases for lower excited electron states of molecules. As a result of such detailed Hund’s classification, more than 30 different coupling schemes (Hund’s subcases) are constructed for rotational Rydberg states of molecules. The conditions of their realization are indicated in terms of the relative quantities of intramolecular interactions, for which analytical estimates are presented. For a large number of subcases, analytical expressions for the molecular matrix elements are found. These expressions can be useful in classification of the experimental spectra of highly excited molecules. As an application, for each of the subcases considered, analytical expressions are given, which describe the linear Zeeman effect and the Paschen-Back effect.

Changes of Normal Coordinates and Geometrical Parameters of a Molecule in a Laser Field

General formulas are derived that describe the changes in equilibrium distances, valence angles, and vibrational frequencies of a polyatomic molecule in a strong laser field. It is shown that the coordinates of normal vibrations do not change in the second order in the field strength. For a nonlinear triatomic molecule of the type of A2B, the changes of geometrical characteristics and vibrational frequencies are obtained in an explicit form.

Charge distribution of the Kr ions resulting from the X-ray irradiation at 1.3 keV

The model of effective atomic potential and the Monte Carlo method are used to calculate the charge distribution of the Kr ions that are formed due to irradiation of neutral atoms by X-ray photons at an energy of 1.3 keV. The calculated results are in good agreement with the recent experimental data and can be used for development and maintenance of gas detectors that monitor the intensity of X-ray free-electron lasers.