Gaunt factors for free-free transitions in the fields of positive ions of carbon,nitrogen, and oxygen,calculated in the scaled thomas-fermi approximation

For air plasmas of higher temperature (1.5–2.5 eV) at normal pressure an essential part of the continuous opacity in the visible and near ultraviolet region is generated by free-free transitions of electrons in the fields of positive ions of carbon, nitrogen, and oxygen. Since the hydrogenic approximation leads to values for the thermally averaged Gaunt factor which are significantly too low, calculations are performed by means of the Scaled Thomas-Fermi approximation and compared with other theoretical results.     

Additive scheme for molecular polarizabilities,calculated in the CNDO approximation

Theoretical and Experimental Chemistry -     

Accurate zero-field mobilities of atomic ions in the rare gases for calibration of ion mobility spectrometers

The zero-field mobilities of many atomic ions in rare gases are calculated from highly accurate, ab initio potential energy curves. They are expected to be accurate to at least 0.05%, thus allowing them to be used to calibrate mobility measurements in different drift-tube and ion mobility mass spectrometers.     

Evidence for the existence of two kinds of orthopositronium in condensed rare gases and for irreversible transitions between them

With reference to time-differential measurements of the momentum distribution of annihilating positron–electron pairs (AMOC) in the condensed rare gases Ne, Ar, and Kr, the paper discusses the question whether in condensed matter positronium (Ps) forms only at predetermined trapping sites or “anywhere”, with subsequent processes leading to Ps trapping or to the formation of Ps bubbles. Ne, in which Ps bubbles are formed not only in the liquid but also in the solid state, may serve as model material for more complex Ps-formers, such as polymers.     

Vibrational transitions of the 7LiH+ ion calculated without the Born-Oppenheimer approximation and with leading relativistic corrections

We recently presented very accurate calculations of the fundamental vibrational frequency of the (7)LiH(+) and (3)He(4)He(+) ions [Stanke et al. Phys. Rev. A 79, 060501(R) (2009)] performed without the Born-Oppenheimer approximation and included leading relativistic corrections. The accuracy of those calculations was estimated to be of the order of 0.06 cm(-1). In the present work we extend the calculations to the remaining pure vibrational states of (7)LiH(+) and similarly accurate results are generated. They may lead to the experimental search for still unidentified lines corresponding to those transitions.     

Vibrational structure in inner-shell ionization of co calculated with the sudden approximation

The vibrational structure of the inner-shell ionization ESCA spectrum of CO is studied. Potential energy curves, force constants, Franck-Condon factors and bond length changes are calculated. Results are discussed within the framework of the transition operator and sudden approximation formalisms.     

The long-range non-additive three-body dispersion interactions for the rare gases, alkali, and alkaline-earth atoms

The long-range non-additive three-body dispersion interaction coefficients Z(111), Z(112), Z(113), and Z(122) are computed for many atomic combinations using standard expressions. The atoms considered include hydrogen, the rare gases, the alkali atoms (up to Rb), and the alkaline-earth atoms (up to Sr). The term Z(111) arising from three mutual dipole interactions is known as the Axilrod-Teller-Muto coefficient or the DDD (dipole-dipole-dipole) coefficient. Similarly, the terms Z(112), Z(113), and Z(122) arise from the mutual combinations of dipole (1), quadrupole (2), and octupole (3) interactions between atoms and they are sometimes known, respectively, as dipole-dipole-quadrupole, dipole-dipole-octupole, and dipole-quadrupole-quadrupole coefficients. Results for the four Z coefficients are given for the homonuclear trimers, for the trimers involving two like-rare-gas atoms, and for the trimers with all combinations of the H, He, and Li atoms. An exhaustive compilation of all coefficients between all possible atomic combinations is presented as supplementary data.     

Thermodynamic properties of individual ions, calculated in terms of conception of real thermodynamic properties of individual ions in solutions

Real and chemical thermodynamic characteristics for several ions in mixtures of water with organic solvents of different classes are calculated on the basis of the proposed conception of real thermodynamic properties of individual ions in solutions. This conception is an improved and generalized version of the procedure for describing thermodynamic activity of individual ions in aqueous electrolyte solutions, which was successfully exploited for many years. The offered methodology enables one to determine thermodynamic characteristics of individual ions both in aqueous and nonaqueous electrolytes. The use of the Volta potential differences for determining real and chemical thermodynamic characteristics of individual ions in solutions is validated.     

Multiple magnetic phase transitions,dilute Fe hyperfine fields and europium valence instabilities in RMn2Si2-xGex,R=rare earth

Mössbauer studies of dilute⁵⁷Fe and¹⁵¹Eu in RMn₂Si_2-xGe_x (R=La, Sm, Eu and Gd) at temperatures 4.2 K to 480 K have been performed. The diamagnetic iron and europium reveal the magnetic order of the Mn and rare earth sublattices through transferred hyperfine interactions. The⁵⁷Fe studies show that in LaMn₂Si₂, LaMn₂Ge₂, and SmMn₂Ge₂ the Mn is magnetically ordered above the known Curie temperatures, and the compounds are antiferromagnets up to T_N=470 K, 415 K and 385 K respectively. Studies of¹⁵¹Eu in R_1-xEu_xMn₂Si₂, (R=La, Gd) display Eu subspectra corresponding to Eu²⁺, Eu³⁺ and intermediate valant Eu. All display large magnetic hyperfine fields.     

Threshold photoelectrons coincidence spectroscopy of the rare gases Ne,Ar, Kr and Xe

Threshold single photon double ionisation of the rare gases neon, argon, krypton and xenon has been studied in an electron-electron coincidence experiment. A new technique has been used where only near-zero energy electrons are detected and these are measured in coincidence. The spectrometer used here employs the penetrating field technique which provides very high detection efficiency, sensitivity and energy resolution. Relative partial double ionisation cross sections have been measured at threshold for then p⁴(³P,¹D and¹S) states of Ne⁺⁺, Ar⁺⁺, Kr⁺⁺ and Xe⁺⁺ and then sn p⁵ (³P and¹P) states of Ne⁺⁺, Ar⁺⁺ and Kr⁺⁺. The observed relative cross sections are in general agreement with a propensity rule for excitation of these states, except for the case of neon.     

Ion-pair states in the complexes of iodine molecule with rare gases

The luminescence excitation spectra and the luminescence spectra of the I₂ + Rg (Rg = He, Ar, Xe; p _Rg = 2–20 Torr) mixtures measured at room temperature by the method of double optical resonance in the spectral range corresponding to the population of the I₂(f0 _g ⁺, v _f = 8.9) levels and in its vicinity are analyzed in this work. The experimental data and their interpretation, according to which these spectra can be explained by the energy transfer in the intermediate I₂(B0 _u ⁺) and final I₂(f0 _g ⁺) states of the free iodine molecule rather than by the optical population, luminescence, and predissociation of the ion-pair RgI₂(IP) complexes, are discussed. It is shown that these data can be explained only with account taken of the optical population of the RgI₂(IP) complexes. Original Russian Text ? M.E. Akopyan, S.S. Lukashov, S.A. Poretsky, A.M. Pravilov, 2009, published in Zhurnal Fizicheskoi Khimii, 2009, Vol. 83, No. 1, pp. 132–141.     

The spectroscopy of molecular reaction intermediates trapped in the solid rare gases

The trapping of neutral and electrically charged molecular reaction intermediates in the solid rare gases and the characterization of these intermediates by vibrational and electronic spectroscopy are surveyed. Spectral data for reaction intermediates trapped in solid neon and argon are compared with the corresponding data obtained from gas phase studies and from quantum chemical calculations. Emphasis is placed on recent progress, including the production, stabilization, and spectroscopic study of highly reactive small molecular ions and the use of ab initio and density functional calculations for the identification of reaction intermediates.     

Ultrasonic frequencies calculated for the q[100] mode in the first-order, tricritical and the second-order phase transitions of NH4Cl.

This study correlates the volume changes to the ultrasonic frequencies of the q[100] mode of NH4Cl for the first-order, tricritical and the second-order phase transitions in this crystal. Using these correlations we were able to calculate the ultrasonic frequencies of this mode at the pressures of 0, 0.6 and 1.1 kbar (first-order), 1.6 kbar (tricritical) and 2.15 kbar (second-order) by means of the volume change data from the literature. Our calculated frequencies are in good agreement with the observed data for the phase region below the critical temperature T(C) for the first-order, tricritical and the second-order phase transitions in NH4Cl. Above T(C) our calculated frequencies do not agree satisfactorily for the q[100] mode and it is incapable of explaining the observed behaviour of NH4Cl. Our method of calculating the ultrasonic frequencies is presented.     

Relativistic oscillator strengths for excited state transitions in some ions of the silver isoelectronic sequence

The relativistic quantum defect orbital method has been applied to the study of fine structure 5p ² P-nd ² D and 5p ² P-ns ² S (n5) transitions (some of them involving highly excited upper levels) in the silver isoelectronic sequence. The resulting oscillator strengths are analyzed in terms of other relativistic results and some available experimental data.     

Measurements of the electronic excitation in atomic collisions of potassium with the rare gases

Excitation cross sections for the potassium 4²P_{$\text{1}\text{2}$} and 4²P_{$\text{3}\text{3}$} states produced in collisions with rare gases are reported. They have been measured by the lightly yield as a function of the energy from 100 to 2500 eV. In addition to this, a spectral analysis from 3300 to 8600 Å of the light is given for some energies. This spectral analysis gives experimental evidence that the excited and ionized states of both potassium and the rare gases are involved in the collision process.     

Structures of some polyfluorinated allyl cations calculated by the MO LCAO SCF method in the MNDO approximation

The MO LCAO SCF MNDO method has been used to calculate the structural features and charge distribution of perfluoroallyl cations substituted in positions 1 and 2. Theoretical and calculated results are compared, and the effect of the nature and position of the substituents on the relative stabilities of the species studied is considered.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 7, pp. 1584–1590, July, 1990.