Multi-band spectral structure and kinetics of the third continua in Ar,Kr and Xe gases excited by a pulsed discharge

Time-resolved VUV-UV emission of Ar, Kr, and Xe gases (Rg), excited by a pulsed discharge, have been measured to clarify the origin of the 3rd continua. Several detected continuum bands exhibit very different time behaviors due to various atomic (ionic) precursors and plasma kinetics. Imaging experiments with ns-gated ICCD camera have shown that the 2nd continua (Rg₂^*) and Rg^* lines emit uniformly in the positive column of the discharge. However, the 3rd continua and Rg^+* lines were excited exclusively in the negative glow zone, where high-energy electrons are injected from the cathode layer. The multi-band structure of the 3rd continua has been connected with Rg²⁺ ions produced in the ground and different excited states. These precursors lead to the formation of several bound states Rg₂^2+*, which decay radiatively to the repulsive states (Rg⁺ + Rg⁺), where Rg⁺ ions can be on ²P_3/2, ²P_1/2 levels due to spin-orbit coupling. The rate constants for the formation of Rg₂²⁺ excimers in three-body reaction and two-body collisional quenching of Rg^2+∗ ions have been determined from the time behaviors of emission. The quenching of Rg^2+∗ ions is explained by the level crossing between bound (Rg^2+* + Rg) and repulsive (Rg²⁺ + Rg) potential curves.     

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.     

Inelastic processes in the scattering of metastable rare gas atoms at metal surfaces

Electron spectra of various metastable rare gas atoms systematically measured on a Pt(111) surface with Rb coverages ranging from submonolayers (3%) to multilayers are presented. The different decay channels of the excited particles are discussed in terms of resonant electron exchange processes between the substrate and the projectile in relation to the work function. It is shown that below a certain value of the work function a highly excited negative rare gas atom is formed which can undergo different de-excitation processes. A careful discussion of the branching ratios into the decay channels offers a natural explanation of the variations in the electron spectra induced by alkali metal adsorption. Additionally, an attempt is made to extract information about the alkali metal chemisorption state from the observed electron spectra.     

Spektroskopische Untersuchung unelastischer Stöße zwischen Ionen oder metastabilen Atomen der Edelgase und Alkalimetallatomen bei thermischen Stoßenergien

The present work deals with the spectroscopic investigation of Penning ionization and nonresonant charge exchange due to thermal-energy collisions of metastable atoms or ions of the inert gases He, Ne with atoms of alkali metals K, Rb, Cs in a low temperature plasma of the corresponding binary mixtures. The rate constants of these reactions and partial rate constants of exciting several alkali metal ion levels were determined by the kinetics of the decay of ionized and excited particles in the afterglow of a pulsed discharge. Measured Penning and charge exchange constants are in order of 10^10-9 cm³ sec^?1. Partial Penning constants in the He? Cs system exhibit a small dependence of the energy defect of reaction, whereby an important part of collisions results in excited Cs⁺-states. On the contrary, energy transfer by charge exchange in He? Rb, Cs systems distinguishes by a significant energy defect dependence. Charge exchange from He⁺ to Rb₀ leads above all to He(2³S₁)-atoms and normal Rb⁺-ions. It follows from the metal ion spectrums, that Penning ionization and charge exchange of the investigated systems under utilized conditions represent as processes of selective excitation of alkali metal ions in afterglow and stationary discharge.     

Off-centre effects in the triplet relaxed excited state of impurity ns2 ions in alkali halides

Abstract

An off-centre displacement of an excited ns² ion from a crystal lattice site is studied for Ga⁺, In⁺ and TI⁺ centres in alkali halides at 0.09-5 K by the time-resolved polarization spectroscopy method. A theory is developed, which considers the off-centre effects as a result of the mixing of the impurity ³nsnp and ³npnp excited states by T_1u vibrations.     

Fe II level populations in a hollow cathode discharge

Relative populations of 232 excited levels of the Fe⁺ ion have been measured in a hollow cathode discharge in neon and in argon. The population distribution shows that thermal charge exchange between noble gas ions and ground level Fe atoms is responsible for most of the excited Fe⁺ population. the cross section for thermal charge exchange is enhanced when the excited Fe⁺ final level has the same 3d⁶(⁵D) core configuration as the initial Fe atom ground level.     

Auger electron emission spectra from foil and gas excited carbon beams

Auger electron emission spectra from 2 MeV C⁺ ion excited by collisions with thin carbon foils and Ne gas are presented. The similarity of qualitative features for the C⁺ → C (foil) and C⁺ → Ne spectra indicates the similarity of ionization mechanisms for beam foil and beam gas excitation. The spectra were normalized to the lowest lying Li-like quartet state (1s 2s 2p)⁴P⁰ in carbon by comparison with time delayed foil excited electron decay-in-flight spectra. Comparison to Hartree-Fock calculated transition energies indicates that transitions in three and four electron carbon ions dominate the prompt spectra.     

Structured emission of relaxing systems: molecular excitons in rare-gas crystals

We have computed the emission spectra of relaxing excitated-state systems in solids as a function of the rates of radiative decay (γ) from excited to ground state and non-radiative decay (γ) within the excited state. When these are comparable a pronounced dip is obtained in the central region of the spectrum, which then may have the appearance of two distinct, unrelated emission bands. The computations well reproduce the observed W and M₂ bands in Ar crystals. Accordingly, these arise from the initially excited and near repulsive regions of the A¹Σ⁺ emitting state, respectively.     

Die Anregung des Tochterions Rb+ durch die plötzliche Kernladungsänderung von85Kr,eingebaut in feste Edelgase

By the sudden change of nuclear charge the daughter-ion is excited with a propability of some percent (monopole-excitation). When⁸⁵Kr is trapped in various solids of rare gases, the daughter-ion Rb⁺ acts as a probe: The spectra of emitted photons contain information about the influence of the surrounding solid on the levels of the excited Rb⁺. These spectra have been observed in delayed coincidence with the nuclear process (β-decay); direct excitation by charged particles is excluded. The results are closely connected to the behaviour of the decaying atom in free state and solid krypton: There are narrow bands (the daughter-ion occupies a regular lattice site) and blue-shifted (Δ v) broad bands (emission from daughter-ion displaced to interstitial sites by recoil).Δ v is different in the various solids of rare gases and increases from Ar to Xe; this is due to the various polarizabilities and lattice constants. A theoretical estimate fits well the experimental values. Besides, the experimental results show that the excitation-probability for⁸⁵Kr in Kr is greater than for⁸⁵Kr in Ar or Xe, which also agrees with theoretical estimates. Furthermore, information about the displacement energies of the Rb⁺ in the various solids of rare gases are gained from the ratio of intensities of the narrow bands to that of the broad bands, which are compared to displacement energies gained from rare-gas pair potentials.     

Photoinduced dissociation reactions of silver fluoride cluster ions

Photoinduced dissociation in the ultraviolet region has been investigated for Ag _nF _n-1 ⁺ cluster ions. Photodissociation spectrum of Ag₂F⁺ in the energy of 3.8–5.6 eV exhibits several sharp bands corresponding to the transition to electronically excited states. In this dissociation, only the Ag₂ ⁺ ion was observed as a fragment ion. Theoretical calculation indicates that the parent Ag₂F⁺ ion has a linear Ag-F-Ag equilibrium geometries in the ground and excited states. Since conformational changes by excitation of bending vibration are necessary for the fragmentation of an F atom, this indicates that production of Ag₂ ⁺ from Ag₂F⁺ is a result of internal conversion and following conformational changes.     

Cd(II) line spectrum emission from semiconductive CdS single crystals

A new method of atom or ion excitation is demonstrated using a semiconductive CdS single crystal. The intense light emission of Cd(II) ion is observed at an adequate He gas pressure, in addition to the Cd(I) atomic line spectrum, when the comparatively low pulse voltage of 810 V/cm is applied to the CdS single crystal. The excitation of Cd(II) is the result of the Penning effect and the energy exchange between He⁺ and Cd atom. Also, the line spectrum emissions of Tl, Ca, Ba, Al, and Ag, which are evaporated on the CdS single crystal, can be observed under the pulse voltage. Our excitation method for the ion or neutral atom is unique in that it requires a comparatively low field for operation and no additional heater for thermal vaporization of those elements.     

Neutral beam sputtering of positive ion clusters from alkali halides

Neutral argon atom beams of 15 keV energy have been used to sputter alkali halides and the ejected positive ions have been analysed in energy, mass and angular distribution.

The use of a neutral beam, rather than an ion beam, minimizes surface charge and the deflection of ejected ions by electrostatic interaction with a charged incident beam.

A cluster component of the form K₂Cl⁺, K₃Cl⁺ ₂ and higher members of the series is found for all alkali halides studied.     

Luminescence spectra of solid xenon excited by volume discharge

The luminescence spectra of solid xenon excited by a volume discharge are studied for the first time. The majority of the energy is emitted in the VUV spectral region due to the radiative decay of excitons. A specific feature of the spectra in the UV and visible regions is the complete absence of lines belonging to neutral excited particles (one-center Xe* and two-center Xe ₂ ^* excitons) and to diatomic Xe ₂ ⁺ ions. Numerous lines of the Xe⁺ ion are shifted by 0.1–0.3 nm with respect to their positions in the gas; the larger the shift, the stronger the distortion of the line shape. Based on the data obtained, a mechanism by which solid xenon is excited and ionized by fast drifting electrons is proposed.     

Excitation of Doubly‐Charged Ion Emission Lines from a Grimm‐Style Glow Discharge Plasma—Comparison Between Yttrium and Zirconium

Spectra of yttrium and zirconium emitted from a Grimm‐style glow discharge plasma were investigated to elucidate the excitation mechanism of doubly‐charged ionic lines when using argon–helium mixed gas as well as argon gas alone. The energy sum for exciting doubly‐charged ion species of yttrium is slightly smaller compared to the case of zirconium, which yields an interesting correlation in the excitation energy between their ionic species and excited species of helium or argon. The Y III emission lines which were assigned to the 4p⁶5p–4p⁶5s(4p⁶4d) transitions could be observed in the argon–helium mixed gas plasma, but those were hardly excited with argon gas only. The Zr III emission lines did not appear in the spectra emitted by the argon gas plasma nor by the mixed gas plasma. A possible explanation for these phenomena is that the excitation of these ionic species is caused principally by collisional energy transfer from helium species to the analyte atoms.     

Zum Lumineszenz-Abklingverhalten von ZnS/Cu

The decay characteristics of ZnS/(10^?4) Cu have been investigated by ion pulse excitation. The excitation density could be varied by using ions of different masses. The decay is exponential. The decay times depend on the ion pulse duration and on the penetration depth of the used ions. The green emission shows two different decay times. The intensity of the slower component of the green emission could be altered by excitation with UV-light before decay measurement. In the case of the slower component of the green emission we suppose an interaction between the excited states of the luminescence centres and energetically deep electron traps.     

Absorption,emission and lifetime data on Cu+ in some alkali halides

The lifetime of the 3d⁹4s→3d¹⁰ transition of Cu⁺ in several alkali halides has been measured as a function of temperature from L.He.T. (?8 K) to R.T. Original instrumentation was developed allowing the automatic continuous recording, as a function of temperature, of single decay time constants even if varying at a rather high rate. Accurate fixed-point measurements by the single photon technique were also performed at R.T., L.N.T. and L.He.T. Two regions of variation of τ versus T have been observed. The interpretation which seems more plausible is that the Cu⁺ ion in its relaxed excited state is essentially in-center in the lower temperature region while for T >40 K it goes off-center even if not so strongly as in the ground state. In NaCl the behaviour of Cu⁺ is quite similar with the difference that in the ground state it is in-center over the whole temperature range from L.He.T. to R.T.     

Auger spectra of aluminium and magnesium induced by caesium-ion bombardment

A caesium ion beam has been used to excite electron emission from Mg, Al, AlAs and GaAs. The portions of the electron emission spectra that result from Auger transitions are compared with previously reported spectra generated with different primary ion beams. It is observed that 10 keV Cs⁺-ion bombardment produces very few excited ions with two 2p vacancies. Evidence for two atomic-like peaks discussed by previous authors, but not unambiguously identified, is also presented.     

Size-dependent light emission from mass-selected clusters

The emission of photons in the visible wavelength range from mass-selected Ag⁺ _n, Cu⁺ _n, Pt⁺ _n and Pd⁺ _n () clusters is observed. Photons are detected 10^-4 s after the cluster generation in a sputter source. The emission intensities display distinct variations with cluster size and material. The observations are interpreted in terms of the decay of metastable states which are excited during the high-energy sputtering process used for the generation of these clusters. Received: 28 October 1997 / Revised: 5 January 1998 / Accepted: 30 January 1998     

A comparison of radiation from sputtered atoms with radiation from projectiles scattered on oxidized magnesium at varying angle of incidence

The intensity of light emitted from sputtered atoms and neutralized, scattered primary ions, excited during 4 keV Ne⁺ and Ar⁺ bombardment of oxidized magnesium has been measured as a function of the incidence angle. It was found that the photon yield of sputtered atoms increases with the angle of incidence much more rapidly than the theoretical sputtering yield and the photon yield of scattered projectiles. In order to explain the experimental results a numerical approach was made based on the following assumptions: (1) the sputtered atom can be excited when it crosses the surface after getting the momentum from the collision cascade; (2) at oblique incidence the sputtered excited atom can be directly emitted after a gentle collision between the incident ion and the surface atom; (3) the neutralized primary ion can only be excited in a violent collision with the surface atom.     

HgCl (B-X) Chemiluminescence from Alkali Atom - HgCl2 Reactions

Laser action on the B²Σ⁺ _1/2 → X²Σ⁺ _1/2 band of HgCl at 557.6 nm (v′=0→v″=22) has previously been achieved under a variety of electronic and optical excitation mechanisms. This letter describes a chemical mechanism for producing excited HgCl. We report on the gas phase reaction between alkali atoms (K, Rb, and Cs) and HgCl₂ which produces HgCl (B-X) emission.