Xe Collisions Research Articles

Rotational energy transfer in Na*2–Xe collisions: Level to level dynamics

Using the method of laser fluorescence we have measured thermally averaged rate constants for rotation changing collisions of Na*2 (A 1Σ) with Xe at six values of initial rotational quantum numbers ranging from 16 to 74. We propose a new scaling law based on the T matrix formalism which fits all these rates to within 20%. This scaling law shows that the square of the T matrix has a power law dependence on the amount of energy transferred, and that mj is conserved in the collision.

Ultraviolet emission in Xe + Xe collisions near threshold

Absolute cross sections have been determined for the vacuum-ultraviolet emission of Xe + Xe collisions between 10 and 15eV. The exponential energy dependence and the low absolute cross section (10 p–5 to 10 –8 A 2) indicate that a direct crossing is not reached.

Inelastic-energy-loss measurements of multipleN- andM-shell excitations in 0.3- to 1.2-MeVXe+-Xe collisions

The inelastic energy losses for single collisions of ${\mathrm{Xe}}^{+}$ ions with Xe targets have been measured for incident ion energies from 0.3 to 1.2 MeV and for scattering angles from 3\ifmmode^\circ\else\textdegree\fi{} to 20\ifmmode^\circ\else\textdegree\fi{}. The energy losses were found to range from 1 to 11 keV with distinct steps at distances of closest approach of 0.22 and 0.12 \AA{}. By comparing these data with earlier ionization data by the same authors these steps are shown to be caused by $M$-shell excitation. Other excitations observed in the ionization data may be attributed to $N$-shell excitation. The distances of closest approach at which these excitations occur agree well with calculations by Eichler and Wille and co-workers, giving further evidence of the usefulness of Fano and Lichten's one-electron molecular model and these calculations.

Collision-induced ion-pair formation of the thallium halides TlF and Tl2F2

Absolute cross sections have been determined for collision-induced ion-pair formation (polar dissociation) of TlF and Tl2F2 from collisions with Xe and Kr atoms. A crossed-beam method was used in which the Xe or Kr atoms were aerodynamically accelerated to energies up to 17 eV (in the laboratory frame). Time-of-flight mass spectrometry permitted the determination of partial cross sections for each positive and negative ion channel in the collision. The cross sections for both monomer and dimer thallium fluoride were considerably smaller than those previously reported for thallium chloride, the difference most likely resulting from the poor energy transfer into the molecular target due to the light F atom. The cross section for the reaction Xe(Kr)+TlF→Xe(Kr)+Tl++F− exhibited, near threshold, a power-law rise with increasing energy σ =const.× (Etot−E0)n/Erel, where Etot is the total collision energy (kinetic plus internal), E0 is the threshold energy, Erel is the relative kinetic energy and n=1.85(1.95). The cross section for rearrangement ionization Xe +TlF→TlXe++F− exhibited a step behavior. Collisions of Xe with the dimer Tl2F2 resulted in both Tl2F++F− and Tl++TlF−2 ion products, the cross sections for the latter ion pair being about one third those for the former. With new values of the heats and entropies of formation of Tl2Cl2, Tl2Br2, and Tl2I2 the absolute cross sections for the previously reported reactions of the dimers Xe(Kr)+Tl2X2→Xe(Kr)+Tl2X++X− have been recalculated. The threshold behaviors of these reactions have also been analyzed in terms of the above power law, giving values of the power n in the range 2.1–2.7. Model calculations have been performed to determine bond energies of the (Tl–X–Tl)+ and (X–Tl–X)− ions, which were used to determine theoretical thresholds for the formation of these ions. The difference between the experimental and theoretical thresholds then gives the internal excitation of the molecular ions at threshold (assuming the inert gas atom carries away negligible energy). Tl2F+, in particular, is formed at threshold with considerable internal excitation (∼1.8 eV). The low cross sections for both TlF and Tl2F2 and the high internal excitation of Tl2F+ at threshold are consistent with a collision model in which only very dynamically constrained collisions result in the extraction of the light F− ion from either TlF or Tl2F2.

Yield of2pσmolecular-orbital x rays in heavy-ion collisions

This paper examines the spectral yield of molecular-orbital (MO) x rays observed in asymmetric 470-MeV Xe collisions. According to a proposal by Heinig et al., x-ray transitions to $2p\ensuremath{\sigma}$ vacancies occurring during the collision give an intense continuum spectrum which falls off rapidly above the $K$ x ray lines emitted by the heavier collision partner. Dynamical calculations of the $2p\ensuremath{\sigma}$ MO x-ray thick-target yield indeed agree within a factor of 3 with the observed intensity. The velocity and impact-parameter dependence of $2p\ensuremath{\sigma}$ MO x-ray production are discussed.

Abnormal broadening of boron emission lines in glow-discharge lamps: evidence for excitation in low-energy B-Ar(Kr or Xe) collisions

The profiles of the boron resonance lines emitted from hollow-cathode and planar-cathode glow-discharge lamps have been studied for a variety of discharge conditions. For discharges operated in argon, krypton or xenon, the lines are extremely broad (halfwidths 0.13-0.27 AA) and are emitted very close to the cathode surface with unusually high intensity. The abnormal linewidths are due to Doppler broadening, which is unusually large because of a preferred excitation for those sputtered boron atoms possessing high kinetic energies of ejection. Investigations of the excitation process suggest that the energetic boron atoms are excited by inelastic collisions with rare-gas atoms. The high excitation efficiency at relatively low collision energies is interpreted in terms of curve crossings, which appear to be particularly favourable for some boron-rare-gas systems.

Diabatic states of the H+-Xe collisional system

Diabatic states of the H+-Xe collisional system have been calculated using the projected-valence-bond (PVB) method. The two lowest diabatic 1 Sigma + PVB states are found to cross at an internuclear distance R=4.7a0. For collision energies E<or approximately=1 keV no transition takes place at this crossing since it is strongly avoided in the corresponding adiabatic energy curves. On the other hand it is shown that Demkov-type transitions occurring at larger distances (R approximately=6.7a0) are responsible for the near-resonant charge-exchange processes in H++Xe collisions. The PVB results, in conjunction with diabatic states for spin-orbit coupling, are used in quantum calculations of differential cross sections. The results are compared with previous theoretical and experimental data.

Total cross sections for Na(3 2P1/2→3 2P3/2) + rare gas collisions

Quantum-mechanical calculations that use the recent pseudopotentials of Pascale and Vandeplanque were employed to obtain the 3 2P1/2→ 3 2P3/2 fine structure transition cross sections for Na+He, Ne, Ar, Kr, and Xe collisions. The collision energy range investigated was from threshold (0.00213 eV) to 0.5 eV. The cross sections are found to rise rapidly from threshold to a plateau, with the Na+Ar, Kr, Xe systems also exhibiting a large secondary maximum at approximately 0.1 eV. Regular undulatory structure was observed superimposed on all the cross sections except for the Na+Ne system, while resonances caused by quasibound states were found to be most prominent on the Na+Ar system. Thermally averaged cross sections were calculated from 100 to 1000 °K and are found to be in reasonable accord with experiment.

Magnetic Splitting of Quasimolecular Electronic States in Strong Fields

The heavy-ion motion in sub-Coulomb collisions generates extreme magnetic fields. The hyperfine splitting of the spin-\textonehalf{} quasimolecular electronic states in U + U is found to reach 10% of the molecular binding energy (100 keV). Also Pb+Pb and Xe+Xe collisions are considered.

A rough estimate of I 7+-Xe collision cross sections by means of the PAC method

The integral PAC attenuation coefficients G 2(∞) measured in gaseous 125,127Xe sources provide a rough estimate of the radioactive ion collision cross section in the thermal energy range.

Excitation transfer, lifetimes, and satellite bands in Cs(7p)–Xe collisions

Observation of the time-dependence of excitation transfer between Cs 7p 2P1/2 and 2P3/2 levels caused by collisions with xenon are reported. The 2P levels were selectively excited with an N2 laser-pumped dye laser, and the spectrum of the fluorescence radiation was observed with 5 nsec time resolution. The lifetimes of the levels were found to be (2P1/2) 154±2 nsec and (2P3/2) 135±2 nsec, and the 2P1/2 to 2P3/2 transfer cross section at 325±10 °K is 0.150±0.002 Å2. An analysis of the time-dependent decay versus xenon partial pressure shows that the cross section for quenching or collision induced radiation is less than 4×10−3 Å2. This demonstrates that collision induced transitions cannot be important in the formation of near red satellites on the Cs 6s–7p lines perturbed by Xe. In addition, the radiative decay constant for the satellite is identical to that for the line within experimental uncertainty. The correspondence of satellite and line decay curves provides a method of identifying satellites with their parent line.

Relaxation of He(31S, 33S, 33P) states in Ne, Ar, Kr and Xe collisions

De-excitation of He(31S, 33S) states by collisions with Ne, Ar, Kr and Xe atoms is mainly attributed to chemi-ionization. For He(33P) states relaxation is attributed to chemi-ionization and a collisional radiative process to He(23S) states.

Magnetic field dependence of the collision transfer rate between m-sublevels

The magnetic field dependence of Hg ∗ (m=0) + Xe → Hg ∗ (m=±1) + Xe collisions in the range from 0 to 15 T has been measured. Additional magnetic field dependent effects were found.

Direct observation of momentum transfer in rotationally inelastic molecular collisions of CO2with H2, D2, He, Ar, Kr, Xe, N2, and CO2

Direct observation of momentum transfer in rotationally inelastic molecular collisions of CO₂with H₂, D₂, He, Ar, Kr, Xe, N₂, and CO₂

Pressure-induced ultraviolet absorption in rare gases: Absorption coefficients for mixtures of Xe and Ar at pressures up to 40 atm in the vicinity of 147 nm

Absorption coefficient κ υ for mixtures of Xe (0.2–20 kg/cm 2) and Ar (5–40 kg/cm 2) has been measured in the range 0.1 cm -1 < κ υ < 40 cm -1. Exponential and power dependencies of κ υ on wavenumber were observed and are discussed. The κ υ-dependencies on the pressure of mixture components are explained by photon absorption at multiparticle collisions of Xe and Ar atoms.

Potential energy curves of the (XeH)+system

Ab initio calculations have been carried out on some potential energy curves of the (XeH)+ molecule, with particular attention paid to the lowest states. The spin-orbit interaction has been taken into account using a semi-empirical method. These calculations suggest the use of a three-state basis when dealing with H+-Xe collisions at low energies. It is also found that the computer MO correlation diagram is in good agreement with that predicted by the 'promotion model' of Barat and Lichten (1972).

Charge Transfer and Fine Structure Transitions in Kr+(2Pj)+Kr and Xe+(2Pj)+Xe Collisions

Charge Transfer and Fine Structure Transitions in Kr⁺(²P_j)+Kr and Xe⁺(²P_j)+Xe Collisions

Penning ionization electron spectroscopy: Ionization of noble gases, Hg, NO, C 2H 4, C 3H 6 and C 6H 6

Energy distributions of electrons released in ionizing collisions of Ar, Kr and Xe with excited metastable atoms of He and Ne, and of Hg, NO, C 2H 4, C 3H 6 and C 6H 6 with excited metastable atoms of Ar have been measured. An apparatus with high energy resolution was used. Shifts of electron energy are discussed in terms of transformation of collision energy into electron energy and in terms of associative ionization as a parallel reaction to Penning ionization. The dissociation energy of ArHg + ions is estimated. The results of ionization of Hg are used to determine the relative population of the 3 P 0 and 3 P 2 metastable states of Ar formed by electron impact, and to detect and measure the energy of the long-lived excited states of N 2 in a beam.

Gas-Phase Recombination of Hydrogen. A Comparison between Theory and Experiment

The modified phase-space theory of reaction rates has been used to calculate the three-body recombination and dissociation rate coefficients of hydrogen in the presence of H2, He, Ar, and Xe collision partners. The theoretical predictions, which rely on semiempirically derived interatomic potential information, are shown to be in excellent agreement with the measured rate coefficients over wide temperature ranges.

Delayed-Coincidence Study ofO+-Xe Collisions at 50-210 keV

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