Resonant collisions of sodium atoms in a laser beam

Excited atoms inside a laser beam can undergo resonant collisions with atoms which are in the ground-state. The total cross-section of resonant collisions exceeds the one for non-resonant collisions by almost three orders of magnitude. An experiment is described which allows to measure the increase of the collision rate in sodium vapor due to the illumination with resonant D-light. In this experiment another phenomenon was observed: Under special conditions the momentum of part of the atoms can be increased considerably by the laser-light.     

Electron capture in collisions of Li~(3+) ions with ground and excited states of Li atoms

The electron capture processes in collisions of Li~(3+)ion with Li(1s~22s)and Li(1s~22p_(0,1))are investigated by using the two-center atomic orbital close-coupling method in the energy range from 0.1 keV/u to 300 keV/u.The interaction of the active electrons with the target ion is represented by a model potential.The present results for the Li~(3+)–Li(1s~22s)system are compared with the available theoretical data and general agreement is obtained for the high collision energies.It is also found that the total and partial electron capture cross sections are sensitive to the initial charge cloud alignment in the low energy region.     

Formation of excited states of atoms and ions in laser plasma from CuInS2

Emission spectra and the energy distribution of the excited-state population density of atoms and ions in erosion laser plasma from CuInS₂ with various crystal-structure orderings are analyzed. It is shown that increased ordering of the target crystal structure causes the excited-state energies of indium atoms generated in the laser erosion plume to increase and that sulfur atoms always emit only in transitions from highly excited states. The ratio of relative ion concentrations in the laser plasma plume is Cu⁺/In⁺/S⁺ = 0.3/0.08/2, which corresponds neither to the atomic ratio of Cu/In/S (1/1/2) in the target nor to the ratio of ionization energies. The results are explained by recombination processes for ions and by the atomization specifics of the CuInS₂ target exposed to long-wavelength radiation. The atomization consists essentially of dissociative processes expressed by CuInS₂ → CuInS + S and CuInS₂ → Cu + InS + S. The electron temperature of polycrystal (single-crystal) plasma at a distance of 1 mm from the target is 0.3 eV (0.4 eV) for atoms and 1.3 eV (2.7 eV) for ions and varies negligibly for plasma up to a distance of 7 mm from the target. __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 75, No. 2, pp. 217–223, March–April, 2008.     

Formation of an alignment in collisions of laser excited sodium with xenon atoms

By photon absorption from a monomode dye-laser beam a spatially ordered velocity distribution (‘atomic beam’) of sodium atoms excited to the 3p ² P _1/2-state, is created. It is predicted theoretically that in collisions of these atoms with atoms of a heavy foreign gas an alignment of the electronic orbital angular momentum is produced. This alignment leads to the appearance of a linear polarization in the sensitizedD ₂-fluorescent light. This polarization is verified experimentally and interpreted in terms of a simplifiedT-operator. It turns out that the scattering distribution for sensitizing collision is of the wide-angle type.     

Muon transfer from excited states of muonic hydrogen atoms studied by X-ray measurement

Muon transfer from proton to deuteron was examined with muonic X-rays. The parameter q _1s was determined directly and the time spectra of the X-rays were analyzed for effects of the muon transfer reaction. This revised version was published online in August 2006 with corrections to the Cover Date.     

Advanced adiabatic approach to superlow-energy inelastic collisions of mesic atoms in excited states

The advanced adiabatic approach previously proposed for describing collision problems in atomic physics is extended to the specific case of mesic-atom collisions in the excited states n≥2. The method and the algorithm of the calculations are described. The calculations of the charge-exchange and Coulomb deexcitation rates in collisions of (pμ)_n, (dμ)_n, and (tμ)_n muonic atoms in the excited states n=3, 4, 5 with the hydrogen isotopes p, d, t are presented in comparison with the conventional adiabatic approach.     

Stark interaction for excited states in alkali atoms,investigated by laser spectroscopy

The scalar polarizability constantα ₀ for excitedS- andD-states in rubidium and cesium was measured utilizing a two-step excitation scheme. An rf lamp and a single-mode dye laser were used to excite the atoms in a collimated atomic beam. Values ofα ₀ were determined for the 9–10² S _1/2 and 7–8² D _3/2 states of rubidium and for the 10–13² S _1/2, 9–10² D _3/2 and 9–11² D _5/2 states of cesium. Further, the isotope shift was evaluated in the 5579 Å rubidium line. A review of experimental polarizability constants for rubidium and cesium is given, and the results are compared with theoretical values.     

Spectroscopy of quasibound states formed by molecular collisions in the presence of a laser

A theory is reported which describes spectroscopic transitions between quasibound states formed during molecular collisions in a laser field. A preliminary calculation suggests that the shapes of absorption lines are sensitive to the shapes of the potentials; hence a method for determining the latter. The calculation also shows that respectable cross-sections for scattering can be obtained at low laser powers.     

Optoacoustic laser spectroscopy of excited vibrational molecular states

A new detection method for absorption from excited vibrational states is suggested, based on optoacoustic detection of weak absorption in a heated gas. Using this method CO₂ laser radiation (λ=9.6 μm) absorption was investigated from excited vibrational states of CO₂, BCl₃, and BF₃ molecules.     

One-electron capture in collisions of fast ions with atoms

The properties of one-electron charge transfer between ions and atomsB ^Z++A →B ^(Z?1)+ A ⁺ are studied at relative velocities of the colliding particles higher than target electron velocities. Calculations of partial and total cross sections in collisions of protons and multiply-charged ions with neutral atoms are performed and compared with experimental data. The universal curve for the capture of the targetK- andL-electrons is given. In all cases at sufficiently high collision energies the electron capture from outer shells decreases and the capture of electrons from inner shells of the target atom becomes predominant.     

Disintegration of argon clusters in collisions with highly vibrationally excited SF6 molecules in crossed molecular and cluster beams

It has been found that collisions of highly vibrationally excited SF₆ molecules (with the vibrational energy E _vib ≥ 0.5–2.0 eV) with Ar _N clusters (where N ≤ 30–40 is the number of atoms in a cluster) in crossed molecular and cluster beams result in capture of molecules followed by complete disintegration of the clusters. Possible applications of the effect for selective doping of clusters with molecules, laser separation of isotopes, and selective transport of molecules to the surface are discussed.     

Inelastic processes in collisions of multicharged fast ions with atoms

We use the eikonal approximation to develop a general formula for the cross sections of inelastic collisions of multicharged fast ions (including relativistic ions) with atoms that is applicable within a broad range of collision energies, has the standard nonrelativistic limit, and becomes, in the ultrarelativistic case, the well-known result that follows from the exact solution of the Dirac equation. As an example we study the excitation and ionization of a hydrogenlike atom, the single and double excitation and ionization of a heliumlike atom, and multiple (up to the eighth order) ionization of the neon atom and (up to eighteenth order) ionization of the argon atom. We derive simple analytical expressions for the inelastic cross sections and establish recurrence relations linking the cross sections of ionization of different orders. Finally, we compare our results with the experimental data. Zh. éksp. Teor. Fiz. 114, 1646–1660 (November 1998)     

Ionization of heavy ions in relativistic collisions with neutral atoms

The problem of ionization of ions in ion-ion and ion-neutral relativistic collisions is considered. Formulas for ionization cross sections are derived in the Born approximation in terms of the momentum transfer without allowance for magnetic interactions. Using these formulas implemented in the LOSS-R code, the ionization cross sections are calculated for the K shells of neutral atoms colliding with protons and also for 1s and 2p electrons of multiply charged heavy ions (nuclear charge Z = 80−90) colliding with bare nuclei and neutral atoms. The calculation results are compared with experimental data and calculations of other authors.     

Fluorescence emission from excited molecular ions in intense femtosecond laser fields

Strong fluorescence emissions were observed for nitrogen, carbon monoxide, and carbon dioxide molecules in intense femtosecond laser fields. These emissions can be assigned to the transitions of the molecular ions from the excited electronic states to the ground electronic states. The formation mechanisms were discussed and the lifetimes were measured for these excited molecular ions in intense laser fields.     

Multiple electron loss by structured heavy ions in fast collisions with complex atoms

A nonperturbative theory of multiple ionization of heavy structured ions in fast collisions with complex neutral atoms is developed. Cross sections are calculated for multiple loss of electrons (up to 15) in collisions of U¹⁰⁺ and U²⁸⁺ with argon atoms and nitrogen molecules. The results are compared with experimental data.     

Scattering of light exotic atoms in excited states

The differential and total cross-sections for the scattering of muonic, pionic, kaonic and antiprotonic hydrogen in excited states from atomic hydrogen have been calculated for the purpose of atomic cascade calculations. The scattering problem is treated in a fully quantum mechanical framework which takes the energy shifts and, in the case of the hadronic atoms, the widths of the ns states into account. The validity of semiclassical approximations is critically examined. Received 4 December 2001 and Received in final form 4 February 2002     

Two-electron transitions in collisions of fast multiply-charged ions with helium-like atoms

Single and double excitation and ionization of a helium-like atom are considered based on the eikonal approximation. Simple analytical formulas are derived for the cross sections of inelastic collision. A comparison with the experiment is conducted. Scientific Research Institute of Applied Physics at Tashkent State University. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 2, pp. 44–48, February, 2000.     

Study of the process of formation of excited states of krypton atomic ions via electron-stimulated desorption of excited molecular ions

The processes of population of excited levels of a krypton atomic ion via electron-stimulated desorption are studied. The radiation yield per single exciting electron in the corresponding krypton spectral lines is measured by the optical time-of-flight mass spectrometric method. The efficiency of the processes studied is compared with that of electron-impact excitation of the same levels.