Charge exchange and Coulomb de-excitation of muonic atoms in low energy collisions

The muon transfer and Coulomb de-excitation rates at the collisions of (pμ) _n , (dμ) _n and (tμ) _n muonic atoms in excited states n = 3, 4, 5 with hydrogen isotopes p, d, t are calculated for all possible combinations of hydrogen isotopes. The advanced adiabatic approach (AAA) [1–3] is adapted and used to the specific case of muonic atom collisions. This revised version was published online in August 2006 with corrections to the Cover Date.     

Coulomb deexcitation of muonic hydrogen within the quantum close-coupling method

The Coulomb deexcitation of muonic hydrogen in collisions with the hydrogen atom has been studied in the framework of the fully quantum-mechanical close-coupling method for the first time. The calculations of the l-averaged cross sections of the Coulomb deexcitation are performed for (μp)_n and (μd)_n atoms in the initial states with the principal quantum number n = 3–9 and at relative energies E = 0.1–100 eV. The obtained results for the n and E dependences of the Coulomb deexcitation cross sections drastically differ from the semiclassical results. An important contribution of the transitions with Δn > 1 to the total Coulomb deexcitation cross sections (up to ～37%) is predicted.     

Ground and excited state dipole moments of coumarin 337 laser dye

This paper reports that the effects of spectral properties of coumarin 337 laser dye have been investigated in different solvents considering solvent parameters like dielectric constant (?) and refractive index (n) of different solvent polarities. The ground state (μ_g) and excited state (μ_e) dipole moments are calculated using Lippert's, Bakhshiev's, and Kawski-Chamma-Viallet's equations. In all these three equations the variation of Stokes shift was used to calculate the excited state (μ_e) dipole moment. It is observed that the Bakhshiev method is comparatively better than the other two methods for ground state and excited state dipole moment calculations. The angle between the excited state and ground state dipole moments is also calculated.     

Transfer of a weakly bound electron in collisions of Rydberg atoms with neutral particles. II. Ion-pair formation and resonant quenching of the Rb(nl) and Ne(nl) States by Ca, Sr, and Ba atoms

Electron-transfer processes are studied in thermal collisions of Rydberg atoms with alkaline-earth Ca(4s ²), Sr(5s ²), and Ba(6s ²) atoms capable of forming negative ions with a weakly bound outermost p-electron. We consider the ion-pair formation and resonant quenching of highly excited atomic states caused by transitions between Rydberg covalent and ionic terms of a quasi-molecule produced in collisions of particles. The contributions of these reaction channels to the total depopulation cross section of Rydberg states of Rb(nl) and Ne(nl) atoms as functions of the principal quantum number n are compared for selectively excited nl-levels with l ? n and for states with large orbital quantum numbers l = n ? 1, n ? 2. It is shown that the contribution from resonant quenching dominates at small values of n, and the ion-pair formation process begins to dominate with increasing n. The values and positions of the maxima of cross sections for both processes strongly depend on the electron affinity of an alkaline-earth atom and on the orbital angular momentum l of a highly excited atom. It is shown that in the case of Rydberg atoms in states with large l ～ n ? 1, the rate constants of ion-pair formation and collisional quenching are considerably lower than those for nl-levels with l ? n.     

Adiabatic hyperspherical approach to describing low-energy mesic-atom scattering

The adiabatic hyperspherical approach developed previously is used to describe the asymmetric mesic-atom scattering aμ+b → aμ+b, a+bμ (a, b=p, d, t) in the collision-energy range 10^?3≤?≤10² eV. Boundary conditions for J≠0 scattering states are formulated, and partial cross sections for J=0–3 are calculated. Effective numerical codes are developed, and a fast convergence of the adiabatic hyperspherical approach is demonstrated: to achieve a precision of about 1% in the calculated cross sections, it is sufficient to use a basis of not more than ten adiabatic hyperspherical functions. The results that we obtained are compared with the previous ones.     

Coulomb Rydberg electron <Emphasis Type="Italic">L</Emphasis>-mixing in collisions with atomic ions

The cross sections of the Rydberg electron L-mixing in a hydrogen atom and a hydrogen-like ion are calculated for slow collisions with atomic ions H*(n, L) + A⁺ = H*(n, L′) + A⁺ without variation of the principal quantum number n. The probability of the L-mixing L → L′ is associated with the quantum interference of the wave functions of adiabatic states, i.e., with the mixing of the time phases of these functions exp(?i∫E _k (t)dt). The effective cross section of such L-mixing for the states with n = 28 are 4–5 orders of magnitude greater than the cross sections determined in previous investigations. The expansion coefficients of spherical Coulomb wave functions in terms of parabolic ones and vice versa, which are necessary for determining cross sections, are calculated on the basis of a comprehensive analysis of the spatial properties of these functions.     

Acceleration of pπ-atoms in a Coulomb de-excitation cascade

An improved adiabatic approach (IAA) previously proposed in atomic physics is extended to the case of collisions of mesic atoms in excited states n⩾2. The computed rates λ _nn′ ^C (E) of the Coulomb de-excitation processes (pπ)_n+p→(pπ) _n′+p are substantially different from the IAA results. It is shown that the Coulomb de-excitation rates λ _nn′ ^C are high enough to explain the appearance of pπ mesic atoms with kinetic energy ∼70 eV, which were observed in [J. E. Crawford, M. Daum, R. Frosch, et al., Phys. Lett. B 213, 391 (1988) and Phys. Rev. D 43, 46 (1991)]. Pis’ma Zh. éksp. Teor. Fiz. 64, No. 3, 129–133 (10 August 1996)     

Investigations of the Spin-Hamiltonian Parameters for the Rhombic Mo5+ Centers in Ca1−x Y x MoO4 Crystal

The spin-Hamiltonian parameters (g factors g _i and hyperfine structure constants A _i , where i = x, y, z) of the rhombic Mo⁵⁺ center in Ca_1?x Y _x MoO₄ crystal are calculated from the high-order perturbation formulas based on the two-mechanism model for the rhombic d¹ tetrahedral clusters with the ground state |d _z 2〉. In these formulas, besides the contributions due to the widely applied crystal-field (CF) mechanism concerning CF excited states, those due to the charge-transfer (CT) mechanism (which is omitted in CF theory) concerning CT excited states are considered. The calculated results are in reasonable agreement with the experimental values. The calculations show that because of the great relative importance of CT mechanism for the components of spin-Hamiltonian parameter along x and y axes, the accurate and complete calculations of spin-Hamiltonian parameters for Mo⁵⁺ and other high valence state dⁿ ions in crystals should take account of both the CF and CT mechanisms. The defect model of the rhombic Mo⁵⁺ center is also confirmed from the calculations.     

Adiabatic Hyperspherical Approach to the Problems of Muon Catalyzed Fusion

The adiabatic hyperspherical approach (AHSA) is applied for the numerical investigation of the scattering processes and resonances in Coulomb three-body mesic atomic systems. The results of the calculations of elastic and inelastic cross sections in low-energy collisions aμ + b (a, b = p, d, t), energies, lifetimes and local characteristics of resonant states of mesic molecular ions ⁿ Heaμ⁺ (n = 3, 4) are presented. This revised version was published online in August 2006 with corrections to the Cover Date.     

Scattering Processes of Excited Muonic Atoms by Molecular Hydrogen

The coupled-channel approach of an excited exotic atom scattering from a hydrogen molecule in the rigid-rotator approximation is developed. The K-matrix method is used to solve the set of coupled collisional equations in the space-fixed (SF) framework for the systems pμ+H₂, dμ+D₂, pμ+D₂, and dμ+H₂. The elastic and Stark mixing cross-sections for scattering on molecular ortho- and para-states are calculated for the principle quantum number n = 2 and collisional energies E≥0.1 eV.     

Measurement of excited state number densities of oxygen and nitrogen in a non-equilibrium plasma

Number densities of several excited states of atomic oxygen and nitrogen have been measured in the decaying non-thermal plasma of a θ-pinch afterglow. The spatial variation of the electron density and temperature as functions of time after initiation of main bank discharge have also been measured to facilitate a comparison of the excited state number densities with model calculations. Measurements of the atomic oxygen excited states indicate that quintet to triplet spin exchange collisions and doubly excited states must be included in the model. The measured populations of the excited atomic nitrogen states agree well with those calculated at high density (N_e≈ 10¹⁴ cm^?3), but disagree badly at lower densities (N_e ≈ 10¹² cm^?3). The discrepancies seem to be real since they are larger than expected measurement uncertainty.     

Heavy-light meson spectroscopy and Regge trajectories in the relativistic quark model

The masses of the ground, orbitally and radially excited states of heavy-light mesons are calculated within the framework of the QCD-motivated relativistic quark model based on the quasipotential approach. Both light (q=u,d,s) and heavy (Q=c,b) quarks are treated fully relativistically without application of the heavy-quark 1/m _Q expansion. The Regge trajectories in the (M ²,J) and (M ²,n _r ) planes are investigated and their parameters are obtained. The results are in good agreement with available experimental data except for the masses of the anomalous $D^{*}_{s0}(2317)$ , D _s1(2460) and $D_{sJ}^{*}(2860)$ states.     

The quenching of Pb(6p 2 1 D 2) atoms in collisions with molecules

The collisions of metastable Pb(6p ^{2 1} D ₂) atoms with various molecules were studied by the diagnostics of radiation from a hollow cathode lamp and a laser on lead vapor. Experiments were performed for a gas flow of lead atoms with argon. The Pb(6p ^{2 1} D ₂) states were excited in a gas discharge in the presence of reagent gas molecules. The absolute rate constants for the quenching and chemical reactions of lead atoms in the ground and excited states were determined. The quantum efficiency of chemical reactions was close to one for the N₂O, CH₂Cl₂, SF₆, and CuBr molecules. Long-lived chemical compounds were formed in these reactions.     

On the mechanisms of formation of excited hydrogen atoms in a decaying helium-hydrogen plasma

We spectroscopically studied the population of the excited hydrogen atomic states with the principal quantum numbers n=3 and 4 in a decaying plasma produced by a pulsed discharge in a mixture of helium (p=40.4 Torr) with a small amount of hydrogen ([H₂]≈10¹² cm^?3). Experiments on recording the response of the spectral line intensities to a short-duration electron temperature perturbation revealed the contribution of electron-ion recombination to the population of the H*(n=3) states in the early afterglow. The ions produced by collisions of hydrogen molecules with metastable He(2³ S ₁) atoms, whose density decreases relatively rapidly with time in the decaying plasma, were assumed to be involved in this process. No population of the H*(n=4) atomic levels due to electron-ion recombination was found. Our experimental results are consistent with the conclusions of previous studies that excitation transfer during collisions of metastable helium molecules with hydrogen molecules plays a major role in the population of the excited hydrogen atomic states both with n=3 and with n=4 during most of the afterglow.     

Photoelectron and electronic absorption spectra of SCl2, S2Cl2, S2Br2 and (CH3)2S2

Photoelectron and electronic absorption spectra of SCl₂, S₂Cl₂, S₂Br₂, and (CH₃)₂S₂ have been measured and analyzed. Quantum chemical calculations (CNDO/ 2 and MWH (Mulliken-Wolfsberg-Helmholtz) have been carried out and the electronic structures have been described in terms of molecular orbital theory. The variation in differential photoionization cross-section as a function of incident photon energy and results of MO computations are used to identify ionization bands and assign ground state MO configurations. Suggested ground state electronic structures coupled with computed virtual MO's are used to interpret the visible and near-ultraviolet electronic absorption spectra. The low energy excited states are described as molecular states followed by the initial members of Rydberg series. Calculated oscillator strengths for molecular transitions are in good agreement with those observed experimentally. Quantum defects, δ, for the Rydberg states have been calculated from the Rydberg equation using the adiabatic first ionization potential.     

Neutral currents and stellar cooling

If weak neutral currents couple with the strengths suggested by recent experiments, then stellar cooling via neutrino pair emission from thermally excited nuclear states may be significant in white dwarfs with central temperature ?10^8° K. At higher temperatures, other neutrino cooling processes are more important. In the sun, the decay of thermally excited ⁵⁷Fe nuclei may produce a moderately large, but probably unobservable, low-energy flux of ν_μ, $\text{g}\text{?}\text{n}{}_{\mathrm{\mu }}$, ν_e, and $\text{g}\text{?}\text{n}{}_{\mathrm{e}}$ neutrinos.     

Theoretical study of highly-excited states of KRb molecule

Semi-empirical adiabatic potential energy curves of highly excited states of the KRb molecule are calculated as a function of the internuclear distance R over a wide range from 3 to 150 a ₀. The diatomic molecule is treated as an effective two-electron system by using the large core pseudopotentials and core polarization potentials. All calculations are performed by using the nonrelativistic CASSCF/MRCI method with accurate basis set functions. The spectroscopic constants of the calculated electronic states agree well with experimental data, including the recent ones from Lee et al., and with available theoretical results.     

Antihydrogen formation in low-energy antiproton collisions with excited-state positronium atoms

The convergent close-coupling method is used to obtain cross sections for antihydrogen formation in low-energy antiproton collisions with positronium (Ps) atoms in specified initial excited states with principal quantum numbers n_i ≤?5. The threshold behaviour as a function of the Ps kinetic energy, E, is consistent with the 1/E law expected from threshold theory for all initial states. We find that the increase in the cross sections is muted above n_i =?3 and that here their scaling is roughly consistent with \({n_{i}^{2}}\), rather than the classically expected increase as \({n_{i}^{4}}\).