A. N. Klyucharev

The Chemi-Ionization Processes in Slow Collisions of Rydberg Atoms with Ground State Atoms: Mechanism and Applications

In this article the history and the current state of research of the chemi-ionization processes in atom–Rydberg atom collisions is presented. The principal assumptions of the model of such processes based on the dipole resonance mechanism, as well as the problems of stochastic ionization in atom–Rydberg atom collisions, are exposed. The properties of the collision kinetics in atom beams of various types used in contemporary experimentations are briefly described. Results of the calculation of the chemi-ionization rate coefficients are given and discussed for the range of the principal quantum number values 5xa0≤xa0nxa0≤xa025. The role of the chemi-ionization processes in astrophysical and laboratory low-temperature plasmas, and the contemporary methods of their investigation are described. Also the directions of further research of chemi-ionization processes are discussed in this article.

The rate coefficients of the chemi-ionization processes in slow Li*(n) + Na collisions

The semi-classical method for determining the rate coefficients of the chemi-ionization processes in slow non-symmetric atom–Rydberg atom collisions is applied to the Li*(n) + Na case. Calculated rate coefficients are compared with the existing experimental data from the literature. Obtained results have confirmed that resonant mechanism of non-elastic processes in atom–Rydberg atom collisions are fully applicable to non-symmetric chemi-ionization processes. The rate coefficients of such processes in Li*(n) + Na collisions are determined in the regions of principal quantum number and temperature 4 ≤ n ≤ 20 and 700 K ≤ T ≤ 1100 K which can be of interest for possible further experiments. Also, the potential curves of several lowest Σ states of the molecular ion LiNa+, as well as the values of the square of dipole matrix element for the transition between X2Σ+- and A2Σ+-states, are presented in this paper.

Influence of inelastic Rydberg atom–atom collisional process on kinetic and optical properties of low-temperature laboratory and astrophysical plasmas

Elementary processes in plasma phenomena traditionally attract physicists attention. The channel of charged-particle formation in Rydberg atom–atom thermal and sub-thermal collisions (the low temperature plasmas conditions) leads to creation of the molecular ions – associative ionization (AI). atomic ions – Penning-like ionization (PI) and the pair of the negative and positive ions. In our universe the chemical composition of the primordial gas consists mainly of Hydrogen and Helium (H, H−, H+, H2, He,He+). Hydrogen-like alkali-metal Lithium (Li, Li+,Li−) and combinations (HeH+, LiH−, LiH+). There is a wide range of plasma parameters in which the Rydberg atoms of the elements mentioned above make the dominant contribution to ionization and that process may be regarded as a prototype of the elementary process of light excitation energy transformation into electric one. The latest stochastic version of chemi-ionisation (AI+PI) on Rydberg atom-atom collisions extends the treatment of the dipole resonant model by taking into account redistribution of population over a range of Rydberg states prior to ionization. This redistribution is modelled as diffusion within the frame of stochastic dynamic of the Rydberg electron in the Rydberg energy spectrum. This may lead to anomalies of Rydberg atom spectra. Another result obtained in recent time is understanding that experimental results on chemi-ionization relate to the group of mixed Rydberg atom closed to the primary selected one. The Rydberg atoms ionisation theory today makes a valuable contribution in the deterministic and stochastic approaches correlation in atomic physic.

On the applicability of the one-dimensional model of diffusion ionization to the three-dimensional Rydberg hydrogen atom in a microwave field

The temporal dynamics of the three-dimensional hydrogen atom under the action of an external electric field is studied by using an analytic model and a numerical simulation. In the stationary case, analytic expressions for determining the evolution of angular momentum L of the Rydberg electron (RE) are obtained and significant oscillations of L are noted. Under conditions of the dynamical chaos regime stimulated by a linearly polarized microwave field, additional specific features of the evolution of L are found with the help of unification of the equations of motion and numerical calculations. The role of L in the formation of diffusion ionization of the RE is revealed.

Dynamics Resonances in Atomic States of Astrophysical Relevance

Ionized geocosmic media parameters in a thermal and a subthermal range of energy have a number of unique features. The photoresonance plasma that is formed by optical excitation of the lowest excited (resonance) atomic states is one example of conversion of radiation energy into electrical one. Since spontaneous fluorescence of excited atoms is probabilistic, the description of the radiating quantized system evolution along with photon energy transfer in a cold atom medium, should include elements of stochastic dynamics. Finally, the chaotic dynamics of a weakly bound Rydberg electron over a grid of the energy level diagram of a quasi-molecular Rydberg complex provides an excitation migration of the electron forward to the ionization continuum. This work aims at discussing the specific features of the dynamic resonances formalism in the description of processes involving Rydberg states of an excited atom, including features in the fluorescence spectrum partially caused by the quantum defect control due to the presence of statistic electromagnetic fields.

Non-Elastic Processes in Atom Rydberg-Atom Collisions: Review of State of Art and Problems

In our previous research, it has been demonstrated that inelastic processes in atom Rydberg-atom collisions, such as chemi-ionization and (n−n′) mixing, should be considered together. Here we will review the present state-of-the-art and the actual problems. In this context, we will consider the influence of the (n−n′)-mixing during a symmetric atom Rydberg-atom collision processes on the intensity of chemi-ionization process. It will be taken into account H(1s) + H ∗(n) collisional systems, where the principal quantum number is n>> 1. It will be demonstrated that the inclusion of (n−n′) mixing in the calculation, influences significantly on the values of chemi-ionization rate coefficients, particularly in the lower part of the block of the Rydberg states. Different possible channels of the (n−n′)-mixing influence on chemi-ionization rate coefficients will be demonstrated. The possibility of interpretation of the (n−n′)-mixing influence will be considered on the basis of two existing methods for describing the inelastic processes in symmetrical atom Rydberg-atom collisions.

Dynamic Characteristics of Excited Atomic Systems

The dynamics of excited atom interactions with other atoms, which often lead to associative ionization, is largely governed by stochastic diffusion of the valence electron through Rydberg states prior to the ionization. Such processes are associated with random changes of the energy state of the highly excited electron, and they are likely to influence the nuclear dynamics, especially at subthermal collision energies. Possibilities of manipulation of the chaotic dynamics of Rydberg states require a detailed exploration. For an electron in a given Rydberg state moving in a microwave field, which can be generated via interaction with another atom or molecule, there exists critical field strength, above which motion of the electron in the energy space is chaotic. Recently a way to block the dynamic chaos regime was shown, if a given Rydberg state is located somewhat above the middle between the two other states with the orbital quantum number differing by one, whereby level shifts can be controlled by employing Stark/Zeeman shifts in external DC electric/magnetic fields. The stochastic effects in collisions involving Rydberg particles, in which the initial and final reaction channels are connected via intermediate highly excited collision complexes with multiple crossings of energy levels, can be treated using the dynamic chaos approach (Chirikov criterion, Standard and Keppler mapping of time evolution of the Rydberg electron, solution of the Fokker-Plank- and Langevin-type of equations, etc.). Such approach to obtaining dynamics characteristics is a natural choice, since the treatment of Rydberg electron dynamics as a kind of diffusion process allowing one to bypass the multi-level-crossing problem, which can hardly be solved by conventional quantum chemistry methods.

Chemi-ionization Processes. Alkali-metal Geocosmical Plasmas

Chemi‐ionization processes, leading to formation of molecular ions, can play an essential role in the sequence of ion‐molecular reactions on surfaces of solid particles or in associative processes of the binary collisions leading to surprising variety of molecular formations in interstellar gas and geocosmical plasmas. The presented results may be recommended for the interpretation of experimental data and for theoretical research of geocosmical plasmas, first of all the the volcanic gases on Io.