Stabilization of diatomic products in recombination of heavy ions

We have studied the kinematic conditions for the formation of the most stable products of direct three-body recombination of ions Cs⁺ and Br^? in the presence of a third-body Xe atom. As the energy of the ions?? central encounters and the energy of the third body range from 1 to 10 eV, the minimal residual energy of the recombination products is found to lie in the interval 0?C0.7 eV. The formation of the recombination products with the minimal internal energies is yielded by collisions of the three particles in a triangular configuration in an impact parameter range from 0 to 2.7 a.u. The mutual orientation angles of the vector of the relative ion velocity and the vector of the third body velocity affect the formation of products with the minimal internal energy rather slightly. In most cases, stabilization of the CsBr molecules and high efficiency of the energy transfer to the third body are observed in configurations of the closest approach of the particles with interionic distances close to the equilibrium distance in the CsBr molecule.     

The dynamics of direct three-body recombination of ions

The trajectory simulation of the direct recombination of the Cs⁺ and Br^? heavy ions in the presence of third-body atoms R = Kr, Xe, Hg was performed on the potential energy surface that controlled the dissociation of CsBr induced by collisions with the same R. The results showed that the probability of recombination decreased as the energy of the approach of ions to each other and the energy of a third body with respect to the center of mass of the ion pair increased. Direct recombination proceeds according to at least two mechanisms of the stabilization of the molecule formed. The first mechanism involves the collision of the R atom with both ions at low impact parameters with respect to the center of gravity of the ion pair. In the second mechanism, impact parameters are large, and energy is removed through a collision with one of the ions of the pair. The products formed have a strongly nonequilibrium vibrational distribution and almost equilibrium rotational energy distribution.     

Statistical dynamics of direct three-body recombination of heavy ions in the presence of argon and xenon atoms

Recombination of singly charged heavy Cs⁺ and Br^– ions with stabilization with neutral Ar or Xe atoms was studied by the classic trajectory method in the range of ion collision energy and third body energy from 1 to 10 eV. The elementary reaction of recombination was studied on the potential energy surface (PES), which quantitatively reproduces the experimental results of collision-induced dissociation of CsBr molecules (the reverse of recombination). An analysis of the statistically reliable number of trajectories revealed a complex multifactor dynamics of recombination, which involves various mechanisms whose realization depends both on the mass and energy ratio of colliding particles and on the PES structure and spatial configurations of collision determined by impact parameters, orientation angles, etc. The molecules that formed as a result of recombination have nonequilibrium vibrational energy distributions and rotational energy distributions comparable to equilibrium.     

Mechanism of the direct three-body recombination of atomic ions in a central collision

The detailed dynamics of direct three-body recombination of the Cs⁺ and Br⁻ heavy ions in the presence of the Xe atom as a third body is studied by the quasiclassical trajectory method. A potential energy surface that quantitatively correctly describes the dynamics of the reverse process of ion formation induced by collisions of CsBr with Xe is used. Depending on the impact parameter of the third body, the stabilization of the product molecule proceeds by several different mechanisms. At impact parameters of b _R ≤ 7 au, the stabilization of the nascent molecule is largely controlled the repulsion potential between one of the ions or both the ions and the third body. The energy transferred to the third body does not depend directly on the repulsive potential energy between the ion and the third body. The phase of collision of the ions at the instant of closest approach plays a key role in the process of energy transfer. For collinear collision configurations of the three particles, the ion-Xe shallow potential wells are demonstrated to produce a noticeable effect.     

Strong Enhancement of Electron–Ion Recombination Owing to Free–Bound and Bound–Bound Resonance Transitions

The effect of free–bound and bound–bound resonance nonadiabatic transitions of an electron on electron–ion recombination rates in the plasma of a Ne/Xe and Ar/Xe inert gas mixture has been studied. A kinetic model of recombination has been proposed including energy relaxation in collisions with electrons, resonant electron capture to Rydberg states through three-body collisions of Xe⁺ ions with Ne or Ar atoms and dissociative recombination of NeXe⁺ or ArXe⁺ ions, and n → n' resonance transitions. It has been shown that effective resonance processes occurring in quasimolecular systems sharply increase both the recombination coefficient and the effect of collisions with neutral particles even at quite high degrees of ionization of the plasma.     

Optical pumping of ions in buffer gases

Transient signals measured with a pulsed rf-optical pumping method are used to determine longitudinal relaxation rates for Sr⁺ ions (even isotopes) in noble gas buffers. Depolarization cross sections of the electronic spin in the Sr⁺5² S _1/2 ground state for binary collisions with rare gas atoms are deduced. The results for σ(Sr⁺5² S _1/2) in Ų are (at temperatures between 374 and 449 °K): 2·10^?5(He),4·10^?5(Ne), 5.7·10^?3(Ar), 1.8·10^?2(Kr), and 4.0·10^?2(Xe). These cross sections for the Sr⁺ ion are about two to three orders of magnitude larger than the corresponding ones for the isoelectronic neutral Rb atom. The large increase of the Sr⁺ relaxation rates is explained with the relaxation mechanism of spin-orbit coupling, taking into account two “indirect” effects of the ionic charge: the increase in the gas kinetic cross sections and the more intimate collisions of the Sr⁺ ion with the noble gas atoms. The depolarization is shown to be predominantly due to short-range interactions. A contribution to the relaxation of the Sr⁺ ion from Sr⁺-noble gas molecule formation, induced by three-body or resonant two-body collisions, could not be established for applied pressuresp between 1.5 and 15 Torr of Ar, Kr, and Xe.     

Radiative lifetime of the v′1(3P2) states of the HgAr, HgKr, and HgXe molecules and the probabilities A(v′, v″) of the v′1(3P2?v″0+(1S0) transitions

A semiempirical method of analysis of quasi-molecular terms in conjunction with experimental potentials of interaction of Hg(6(³ P ₁)) atoms with Ar, Kr, and Xe atoms are used to obtain the Hg(6³ P ₂)-Ar, Kr, Xe interaction potential, which are applied to calculating the radiative lifetimes of the v′1(³ P ₂) states of the HgAr, HgKr, and HgXe molecules and the probabilities of the v′1(³ P ₂)−v″0⁺(¹ S ₀) transitions.     

Multiphoton mass spectra of XeKr molecules in the range of excited Xe*6<Emphasis Type="Italic">p</Emphasis>[5/2]<Subscript>2, 3</Subscript> atoms

Data on excited states of XeKr molecules in the energy range 78280–77600 cm^?1 are obtained. Using the method of multiphoton laser photoionization of molecules in a supersonic jet, five vibrational progressions of XeKr molecules are obtained, which are attributed to five electronic-vibrational transitions from the ground state of the XeKr molecule of the symmetry 0⁺ to excited states of the symmetry Ω = 0⁺, 1, 2 with the dissociation limit Kr¹ S ₀ + Xe*6p[5/2]₂ and of the symmetry Ω = 1, 2 with the dissociation limit Kr + Xe*6 p [5/2]₃. The molecular constants of the corresponding excited states of the XeKr molecule are estimated.     

Observation of proximity- and non-equilibrium effects in ternary heavy ion reactions

Kinematically complete experiments have been performed on the two- and three-body exit channels in the reactions⁸⁴Kr+¹⁶⁶Er and¹²⁹Xe+¹²²Sn at 12.5 MeV/u. Three-body events occur with an unusually high probability. They arise from a fast two-step mechanism where a sequential fission-like process follows a deep inelastic collision with preferentially very large energy losses. Strong Coulomb proximity effects are observed in the three-body final state which, treated quantitatively in Coulomb trajectory calculations, establish a time-scale of 1·10^?21 s between the consecutive scission acts. The angular distribution of fission fragments is consistent with an orientation of the fission axis approximately collinear with the axis of the first scission, and the mass distribution of the fission is asymmetric with the heavier mass emitted preferentially opposite to the direction of the third particle. The high fission probability, the short time-scale, the near collinear orientation and the fission mass asymmetry together present consistent evidence for a new phenomenon of non-equilibrium fission.     

Infrared spectra of the Kr—CO and Xe—CO van der Waals complexes

The infrared spectra of the weakly bound complexes Kr—CO and Xe—CO have been studied in the region of the CO stretching vibration (4.7 μm) using a high-resolution tuneable diode laser probe. The complexes were observed in a long path (200 m) low temperature (76 K) gas cell (Kr—CO) and in a pulsed supersonic jet expansion (Kr—CO and Xe—CO). Previous long path cell measurements on these complexes at lower resolution analysed only the K = 0 and 1 stacks of rotational levels in the ground intermolecular vibrational state. The new data extend up to K = 3 (Xe—CO) or 4 (Kr—CO), and also include K = 0 and 1 stacks in the excited bending state, ν₂ = 1. The bending frequencies for Kr—CO and Xe—CO (in the ν_co = 1 upper state) were determined to be 13.156cm_?1 and 13.794cm^?1, respectively. Detailed molecular parameters were determined to describe the rotational energy levels of each complex using a simple empirical Hamiltonian. These results enable parameters to be compared for the entire series of rare gas—carbon monoxide complexes, from He—CO to Xe—CO. Also they will guide the future development and evaluation of accurate intermolecular potential energy surfaces for Kr—CO and Xe—CO.     

The Influence of Admixtures of Molecular Gases on the Efficiency of Radiation Production by Ar?Hg Mixture Plasmas used in Fluorescent Lamps

Starting from former investigations of pure Ar? Hg mixture plasmas in parameter ranges typical of fluorescent lamps we studied the influence of additional admixtures of molecular gases (N₂, H₂) on the energy transfer from the electrons heated by an electric field to the lowest excited states of Hg atoms which are the energy source for the resonance radiation production. By calculation of the different power loss rates via solving the appropriate Boltzmann equation for three component mixture plasmas it was found that already a threshold level of molecular impurities of about 10^?4 Torr leads to a marked energy dissipation by the impurities and thus to a pronounced reduction of the efficiency of the resonance radiation production. This is caused by the great effectivity of vibrational excitation of molecules in electron collisions due to the great cross sections for such collisions and their low thresholds.     

Stay time measurements for Xe,Kr, and CO2 physisorbing on Ni and Cu surfaces

A pulsed molecular beam apparatus is used to measure mean stay times for gases physisorbing on cooled surfaces. Most of the data are for Xe on nickel surfaces. Data are also presented for Kr and CO₂ on nickel, Xe on copper, and Xe on ion-sputter-cleaned nickel. All targets are polycrystalline. Surface temperatures range from 92 to 125 K and measured stay times range from 10^?5 to 10^?3 s. Heats of adsorption and pre-exponential factors deduced from the data indicate that the adsorption is localized (immobile) and suggest that the sputter-cleaned targets may be approximately clean. A model relating the shape of the detector signal to the mean stay time is presented and its validity is assessed. Measured speed distributions for the desorbing molecules exhibit an excess of slow molecules compared to that expected for simple effusion. At lower surface temperatures where longer stay times are observed, a peculiar detector signal dip is observed which appears to indicate that the adsorbing beam pulses temporarily reduce the steady state desorption rate of background atoms.     

Test of the intercombination rules on the two excited states (0 and 1) potential parameters of the second group metal atoms perturbed by inert gases

A set of intercombination rules has been used to calculate the two excited (³0 and ³1) state potential parameters ε₁₂ and R₁₂ of Hg, Cd and Zn interacting with inert gases (Xe, Kr, Ar and Ne). The results obtained with these rules are compared with various experimental and theoretical results for these molecules. The rules can be very well used for determination of the position of the potential minimum for the two states of all molecules. Concerning the well depths of the two states (³0 and ³1) of these molecules, it is observed that for the more bounded excited state ³0 some of these rules give results that are in close agreement with experimental data especially for molecules consisting of heavy atoms but for the shallow excited state ³1 these rules cannot be used.     

Interaction of trapped metastable excited He atoms with solid noble gases,Ne, Ar and Kr,investigated by EPR

Local metastable excited states are found in Ne, Ar and Kr cryocrystals as He gas-discharge products are trapped in the growing cryocrystals. These states are detected by EPR and are interpreted as being local metastable excitednp⁵(n+1)s³P₂ atomic-type states in Ne, Ar and Kr cryocrystals. Analysis of the results allows the following explanation of the observed effect to be given. For the Ne cryocrystal the effect is interpreted as a new phenomenon: quasi-resonance transfer of excitation energy from the metastable He 2³S₁ atom trapped in a growing neon cryocrystal to the exciton energy band of the neon crystal followed by the exciton self-trapping into the 2p⁵3p state and subsequent decay, ending in the 2p⁵3s³P₂ state recorded by EPR in our experiment. In the case of Ar and Kr cryocrystals the effect is explained as being due to an internal ionization of the cryocrystals by the excitation energy of trapped metastable He atoms, which implies the formation in the cryocrytal of a Rg⁺ ion and a free electron in the conduction band, whereupon the fast (of 10^?12 s) self-trapping reaction of a hole follows: Rg⁺+Rg→Rg ₂ ⁺ . Thereafter the dissociative recombination reaction Rg ₂ ⁺ +e→Rg ₂ ^** →Rg+Rg*(³P₂) could take place.     

Penning ionization electron spectroscopy of CO,HCl, HBr and of triatomic molecules N2O,NO2, CO2, COS and CS2

The energy of electrons released in ionization of di- and triatomic molecules by He (2¹S, 2³S), Ne and Ar (³P_{0, 2}) metastable atoms was measured. Attention was concentrated on the determination of peak shifts and peak form in order to elucidate new features of the mechanism of ionization with respect to ionization of atoms. In ionization by He (2¹S) atoms, asymmetric peak forms and greater shifts towards lower electron energy were found than in ionization by He (2³S) atoms. A tentative explanation for peak shifts in terms of orientation of molecules during the collision and of molecular orbitals involved in ionization was proposed. Effects due to J values of metastable atoms and molecular ions were described. The ionization of electronegative molecules (NO₂) probably takes place already at large particle separation because of mixing with the X⁺ABC^? ionic state which, on recombination, ionizes into X + ABC⁺ + e.     

Reliability evaluation for failed fuel identification using resonance ionization mass spectrometry

In the fast reactors, rapid and accurate identification of a fuel failure event is essential for ensuring safety operation. Isotopic analysis of krypton (Kr) and xenon (Xe) using resonance ionization mass spectrometry (RIMS) is an effective identification tool, in which Kr and Xe atoms are resonantly ionized by a pulsed laser at 216.7 nm and 249.6 nm, respectively, and then three isotopic ratios: ⁷⁸Kr/⁸⁰Kr, ⁸²Kr/⁸⁰Kr and ¹²⁶Xe/¹²⁹Xe are measured to detect the location of the failed fuel assembly. In this paper, we report on the required analytical precision of RIMS estimated from simulation studies as well as the analytical performance of our spectrometer to evaluate the availability of RIMS to the failed fuel identification technique in the fast reactors.     

Multiphoton mass spectra of Xe2 molecules in the range of excited Xe*(6p, 5d) atoms

The (2 + 1) photoionization mass spectra of Xe₂ molecules are studied in a supersonic jet upon excitation by laser radiation in the energy range 80321.3–77821 cm^?1, corresponding to the dissociation of the Xe₂ molecule into atoms Xe(¹ S ₀) + Xe*(6p, 5d). Several vibrational progressions are observed, which are attributed to two-photon transitions of Xe₂ from the ground state to the excited states of the O ⁺ _g, 1_g, and 2_g symmetries. Based on the analysis of these progressions, the molecular constants of a number of excited states of Xe₂ are estimated.     

Investigation of electron-beam-excited molecular gas lasers

Physical processes are investigated in active media of high-pressure gas lasers operating on electronic transitions of molecules. Lasing was obtained in the VUV ( = 172 nm) region of the spectrum by exciting compressed xenon and an Ar:Xe mixture. The effect of the temperature and pressure on the kinetics of the processes in the active laser media Ar:N₂, Xe:0₂, and Ar:Kr:F₂ are investigated. A new class of excimers, consisting of one halide and two inert atoms, is observed for the first time ever, and the temperature dependence of the spontaneous and laser emissions of XrF* is investigated; this dependence is due to the redistribution of the energy drawn from the electron beam among the excimers KrF^* and Kr2^F*.Translated from Trudy Ordena Lenina Fizicheskogo Instituta im. P. N. Lebedeva, Vol. 142, pp. 172–202, 1983.     

Accurate ground-state potential energy surfaces of the C2H2–Kr and C2H2–Xe van der Waals complexes

Accurate ab initio intermolecular potential energy surfaces (IPES) have been obtained for the first time for the ground electronic state of the C₂H₂–Kr and C₂H₂–Xe van der Waals complexes. Extensive tests, including complete basis set and all-electron scalar relativistic results, support their calculation at the CCSD(T) level of theory, using small-core relativistic pseudopotentials for the rare-gas atoms and aug-cc-pVQZ basis sets extended with a set of 3s3p2d1f1g mid-bond functions. All results are corrected for the basis set superposition error. The importance of the scalar relativistic and rare-gas outer-core (n–1)d correlation effects is investigated. The calculated IPES, adjusted to analytical functions, are characterized by global minima corresponding to skew T-shaped geometries, in which the Jacobi vector positioning the rare-gas atom with respect to the center of mass of the C₂H₂ moiety corresponds to distances of 4.064 and 4.229?Å, and angles of 65.22° and 68.67° for C₂H₂–Kr and C₂H₂–Xe, respectively. The interaction energy of both complexes is estimated to be ?151.88 (1.817?kJ?mol^?1) and ?182.76?cm^?1 (2.186?kJ?mol^?1), respectively. The evolution of the topology of the IPES as a function of the rare-gas atom, from He to Xe, is also discussed.