Slow Atomic Collisions Research Articles

Collisional Broadening of Spectral Lines in Slow Atomic Collisions

Collisional Broadening of Spectral Lines in Slow Atomic Collisions

Dynamic two-center resonant photoionization in slow atomic collisions

An additional channel for photoionization of an atom A by an electromagnetic field opens if it interacts with an atom B resonantly coupled to this field. In this channel, which is known to be very efficient when A and B constitute a bound system, A is ionized via resonant photoexcitation of B with subsequent energy transfer to A through two-center electron correlations. We show that it can strongly dominate the ionization of A also in collisions with B, even though the average distance between A and B exceeds the typical size of a bound system by orders of magnitude.

Two-center dielectronic recombination in slow atomic collisions

A free electron can form a bound state with an atomic center $A$ upon photo emission (radiative recombination). In the presence of a neighboring atom $B$, such a bound state can, under certain conditions, be also formed via resonant transfer of energy to $B$, with its subsequent relaxation through radiative decay (two-center dielectronic recombination). This two-center process is very efficient in the 'static' case where $A$ and $B$ form a weakly bound system, dominating over single-center radiative recombination up to internuclear distances as large as several nanometers. Here we study its dynamic variant in which recombination occurs when a beam of species $A$ collides with a gas of atoms $B$ and show that, even though the average distance between $A$ and $B$ in collisions is orders of magnitude larger than the typical size of a bound system, the two-center recombination can still outperform the single-center radiative recombination.

Associative ionization reaction N + O → NO+ + e– in slow collisions of atoms

The endothermic associative ionization reaction N(2D) + O(3P) → NO** → NO(1Σ+) +e- in slow collisions of the atoms has been considered in terms of the multichannel quantum defect theory. The dependences of the partial and total cross sections of the reaction on the energy of the colliding atoms in the range of 0–0.3 eV have been calculated. It has been shown that the cross sections have a pronounced resonance structure, which is formed as a result of the multichannel interaction of autoionization states of the intermediate Rydberg complex NO** with dissociative states. The temperature dependence of the reaction rate constant is presented. The results are compared with those of other calculations and available experimental data.

Exact solution of the Bloch equations for the nonresonant exponential model in the presence of dephasing

An exact analytic solution is presented for a two-state quantum system driven by a time-dependent external field with an exponential temporal shape in the presence of dephasing. In the absence of dephasing the model reduces to the well-known Demkov model originally introduced in slow atomic collisions. The solution is expressed in terms of the generalized hypergeometric function ${}_{1}{F}_{2}(a;{b}_{1},{b}_{2};x)$. Various limiting cases are examined in the limits of weak and strong dephasing, strong driving field, and exact resonance.

Reaction of associative ionization [formula omitted] at slow collisions of atoms

The endothermic reaction of associative ionization of nitrogen and oxygen atoms was studied in the case of slow atom collisions in the framework of multichannel quantum defect theory. The diabatic potential energy curves of the NО molecule excited states were calculated using multireference configuration interaction methods implemented in MOLPRO package. It was shown that cross section dependence on the energy of the colliding atoms is in a good agreement with the experiment. The rate coefficient of the reaction was defined at the temperature 100K⩽T⩽1000K range. The obtained data may be used for calculating the tiered kinetics of highly excited Rydberg state population in low-temperature plasma.

Analyticity and the Global Information Field

The relation between analyticity in mathematics and the concept of a global information field in physics is reviewed. Mathematics is complete in the complex plane only. In the complex plane, a very powerful tool appears—analyticity. According to this property, if an analytic function is known on the countable set of points having an accumulation point, then it is known everywhere. This mysterious property has profound consequences in quantum physics. Analyticity allows one to obtain asymptotic (approximate) results in terms of some singular points in the complex plane which accumulate all necessary data on a given process. As an example, slow atomic collisions are presented, where the cross-sections of inelastic transitions are determined by branch-points of the adiabatic energy surface at a complex internuclear distance. Common aspects of the non-local nature of analyticity and a recently introduced interpretation of classical electrodynamics and quantum physics as theories of a global information field are discussed.

Erratum: Theory of slow-atom collisions [Phys. Rev. A54, 2022 (1996)

Erratum: Theory of slow-atom collisions [Phys. Rev. A<b>54</b>, 2022 (1996)

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 chemiionization 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 5 < n < 25. 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.

Associative ionization in slow collisions of atoms

An analysis of the modern theory of associative ionization (AI) is performed, and ways of its further development are discussed. The threshold behavior of the cross section of endothermic AI reactions is considered and it is shown that, in the quantum case, its dependence on the above-threshold energy E is strictly linear, i.e., significantly different from the E 3/2 law ensuing from the semiclassical theory. This has a simple explanation, since the matrix elements of the scattering operator are finite at E = 0 due to the tunneling effect. The possibility of describing the dynamics of an elementary AI event within the framework of the diffusion approximation is substantiated, and the conditions of applicability of the theory of “quantum chaos” to treating the spectrum of highly excited Rydberg molecules are examined. The quantum properties of the exothermic processes of AI and Penning ionization in the case of the states of the interacting atoms being autoionizing are discussed in detail. A comparison with the semiclassical theory is presented.

Multichannel excitation cross sections of sodium atoms at slow collisions with hydrogen atoms

Excitation cross sections at slow collisions of hydrogen and sodium atoms are calculated based on two sets of quantum-chemical data. The results of calculations permit one to conclude that, upon the excitation of the sodium atom from the ground state in the region of near-threshold energies, the cross sections are highly sensitive to matrix nonadiabaticity elements. In addition, the matrix nonadiabaticity element was varied for the transition 3s → 3p of the sodium atom at fixed collision energy near the reaction threshold. It was found that the variation leads to a significant change in the excitation cross section 3s → 3p, and the range of the energetic dependence of this cross section was determined.

Quantum theory of slow atomic collisions

Quantum-mechanical and semiclassical theories of slow atomic collisions are reviewed, with attention to electron-translation factors and their effects.

Change of atomic spins in slow collisions

In the present work, slow atomic collisions with changes of atomic spins are examined. In this case, the electron spin exchange in the process of collisions causes the polarization characteristics of atoms to change. Formalism has been constructed based on the adiabatic approximation and polarization operator technique for a description of changes of arbitrary spins of colliding atoms. Singlet-triplet transitions, analogous to those of inelastic exchange electron scattering on two-electron atoms, are described for collisions of hydrogen and alkali metal (H, K, Na, Cs, and Rb) atoms with two-electron atoms or ions (He, Li +, and Hg). The processes of the type H(2S)+He(1S)→H(2S)+He(3S) and \(P\left( {^4 S_{3/2} } \right) + He\left( {^3 S_1 } \right) \to P\left( {^2 S_{1/2} } \right) + He\left( {^3 S_1 } \right)\) are also considered.

Multichannel quantum-defect theory for slow atomic collisions

We present a multichannel quantum-defect theory for slow atomic collisions that takes advantages of the analytic solutions for the long-range potential and both the energy and angular momentum insensitivities of the short-range parameters. The theory provides an accurate and complete account of scattering processes, including shape and Feshbach resonances, in terms of a few parameters such as the singlet and triplet scattering lengths. As an example, results for $^{23}\mathrm{Na}\ensuremath{-}^{23}\mathrm{Na}$ scattering are presented and compared to close-coupling calculations.

Spin Exchange in Slow Atomic Collisions

In the present work, a pattern of spin polarization is investigated within the framework of nonrelativistic interactions of electrons of colliding atoms. The electron spin exchange in the process of collision causes the polarization characteristics of atoms to change. It is demonstrated that results of collision of hydrogen atoms with alkaline metals (H, K, Na, Cs, and Rb) are analogous to those of elastic exchange electron scattering by single-electron atoms.

Vibrationally resolved collisions in cold hydrogen plasma

Slow collisions (0.5–100eV) of hydrogen atoms and ions with vibrationally excited hydrogen molecules and molecular ions are studied using fully quantal (below 10eV) and semi-classical approaches. Considered transitions include charge transfer, excitation, dissociation, three-body diatomic association, as well as energy and angular spectra of dissociation fragments. Mutual relations of various elastic and inelastic processes, the relevant physical mechanisms governing vibrational dynamics in inelastic channels and comparison of the fully quantal and semi-classical results are also reported.

On the criterion for effectiveness of wave linear transformation in a smoothly inhomogeneous medium and of nonadiabatic transitions during atomic collisions

A universal criterion for effectiveness of linear transformation of waves with locally close characteristic exponents in smoothly inhomogeneous media is obtained. The same criterion is applicable for estimating the effectiveness of nonadiabatic transitions in slow atomic collisions. The formalism developed for an analysis of the linear interaction of waves is based of the WKB asymptotic form of the solution of a scalar nth order ordinary differential equation. The obtained criterion can be applied in any practical problem for drawing a conclusion about the effectiveness of the linear interaction of modes if only the characteristic equation of waves in a homogeneous medium and the coefficients of the initial differential equation are known. In this case, the solution of the problem is reduced to elementary arithmetic calculations.

Angular-momentum-insensitive quantum-defect theory for diatomic systems

With recent developments such as the analytic solutions of the Schrodinger equation for 1/r 6 and 1/r 3 potentials @1-3#, our understanding of two-atom systems is already conceptually comparable to the quantum-defect theory ~QDT! of atomic Rydberg spectra @4#. Namely, the slow atomic scattering and the rovibrational spectrum of a particu- lar angular momentum can be understood in terms of the long-range solutions and a parameter that is a slowly varying function of energy in the threshold region @5-7,1-3#. In this work, we show that a two-atom system possesses an even greater degree of systematics in the following sense. Unlike the QDT for atomic Rydberg spectra in which different angular-momentum states have different quantum defects with no general relationships among them, a single param- eter is sufficient to characterize slow atomic collisions for practically all angular momenta. The same parameter also characterizes the rovibrational spectra in the threshold re- gion, including states of different angular momenta. In other words, in addition to the relationship between the bound spectrum and scattering, as expected from traditional QDT formulations @4#, a two-atom system has also the unique property that scattering of different angular momenta are re- lated, and so are the bound spectra of different angular mo- menta. The origin of this relationship between different angular- momentum states is not difficult to understand and is due to a combination of the following three properties of a typical molecular system. ~i! Atoms are strongly repulsive at short distances. ~ii! Atoms are heavy compared to electrons. ~iii!

Resonant charge exchange with the p-electron transition

The asymptotic resonant charge exchange theory is developed for slow collisions of atoms and ions with valent p-electrons. Because of a small rotation angle of the molecular axis in the course of the p-electron transition, the resonant charge exchange cross section is not sensitive to the rotational energy of colliding particles, and the cross sections are nearly equal for cases “a”, “b”, and “d” of the Hund coupling, and also for cases “c” and “e” of the Hund coupling. The cross sections of the resonant charge exchange process are evaluated under various conditions and for various elements of the periodical table with p-electron shells of atoms and ions.

Inelastic transitions in slow heavy-particle atomic collisions

It is a generally held belief that inelastic transition probabilities and cross sections in slow, nearly adiabatic atomic collisions decrease exponentially with the inverse of the collision velocity $v$ [i.e., $\ensuremath{\sigma}\ensuremath{\propto}\mathrm{exp}(\ensuremath{-}\mathrm{const}/v)].$ This notion is supported by the Landau-Zener approximation and the hidden crossings approximation. We revisit the adiabatic limit of ion-atom collisions and show that for very slow collisions radial transitions are dominated by the topology of the branch points of the radial velocity rather than the branch points of the energy eigensurface. This can lead to a dominant power-law dependence of inelastic cross sections, $\ensuremath{\sigma}\ensuremath{\propto}{v}^{n}.$ We illustrate the interplay between different contributions to the transition probabilities in a one-dimensional collision system for which the exact probabilities can be obtained from a direct numerical solution of the time-dependent Sch\"odinger equation.