Electronic energy transfer between metastable argon atoms and ground-state oxygen atoms

The transfer of electronic energy between metastable argon and ground-state oxygen atoms has been studied in a discharge-flow apparatus. The excitation energy of the argon metastables is transferred to the 3p ³P state of atomic oxygen with a cross section of 3 A². The energy transfer is discussed in terms of an ionic-intermediate, curve-crossing mechanism for which the calculated cross section is 13 A².     

Distribution of metastable argon atoms in the modified Grimm-type electrical discharge

The absorbance by metastable argon atoms of the Ar 696.543 nm line in the modified Grimm-type electrical discharge source was measured at different discharge conditions and at distances varying from 0.25 to 6 mm from the cathode. A uranium/argon hollow cathode lamp was used as primary source, which gave an argon gas temperature of 850 K when run at 12 mA. A maximum absorbance of 0.57 was found 3 mm from the cathode at 600 V, 80 mA. The magnitude of absorbance increases with discharge current while the position of maximum absorbance shifts away from the cathode with increase in discharge voltage. The quenching of metastable atoms by nitrogen is demonstrated.The spatial distribution of the intensity of four different types of spectral lines is shown. The approximate number densities of the different particles are 10¹²cm^?3 for metastable argon atoms, 10¹⁶cm^?3 for neutral argon atoms, 10¹³ cm^?3 for sputtered copper atoms and 10¹⁴cm^?3for electrons.     

Electron impact fragmentation of size-selected krypton clusters

Clusters of krypton are generated in a supersonic expansion and size selected by deflection from a helium target beam. By measuring angular distributions for different fragment masses and time-of-flight distributions for fixed deflection angles and fragment masses, the complete fragmentation patterns for electron impact ionization at 70 eV are obtained from the dimer to the heptamer. For each of the neutral Kr(n) clusters studied, the main fragment is the monomer Kr(+) ion with a probability f(n)(1) > 90%. The probability of observing dimer Kr(2)(+) ions is much smaller than expected for each initial cluster size. The trimer ion Kr(3)(+) appears first from the neutral Kr(5), and its fraction increases with increasing neutral cluster size n, but is always much smaller than that of the monomer or dimer. For neutral Kr(7), all possible ion fragments are observed, but the monomer still represents 90% of the overall probability and fragments with n > 3 contribute less than 1% of the total. Aspects of the Kr(n) cluster ionization process and the experimental measurements are discussed to provide possible reasons for the surprisingly high probability of observing fragmentation to the Kr(+) monomer ion.     

Interaction energy decomposition analysis for formic acid complexes with argon and krypton atoms

Interaction energy decomposition was performed for a series of HCOOH…Rg complexes, where Rg is either argon or krypton, and the formic acid molecule has trans or cis conformation. The decomposition, performed within Symmetry-Adapted Perturbation Theory framework, shows that even if the stability of the complexes is due to significant dispersion contribution, the role of induction and exchange should not be neglected. One of the complexes, which is the lowest energy minimum found, is a ‘hydrogen bond-like’ structure which, with respect to other complexes, exhibits visible changes in the relations between the interaction energy terms, particularly – much more pronounced induction contribution.     

Absolute total cross sections for scattering of hydrogen atoms by argon,krypton and xenon

Absolute total cross sections for scattering of hydrogen atoms by argon, krypton and xenon were measured as a function of velocity in the range from 1.8 to 6.2 km/sec. An analysis in terms of Lennard-Jones (12.6) and (8.6) model potentials leads to estimates of the interatomic forces.     

Vacuum UV emission from reactions of metastable inert gas atoms: Chemiluminescence of ArO and ArCl

Vacuum UV chemiluminescence from bound upper states of ArO, KrO and ArCl is observed from the quenching of excited inert gas atoms by N₂O, O₃, Cl₂ and CCl₄. In these systems, the metastable ³P₂ states of Ar and Kr strongly resemble ground state alkali atoms in their chemical properties.     

Electron impact fragmentation mechanisms of 2,4,6-trinitrotoluene derived from metastable transitions and isotopic labeling

Precursors of the major ions in the electron impact spectrum of 2,4,6-trinitrotoluene have been determined by observations of metastable peaks and isotope shifts. In 2,4,6-trinitrotoluene with adjacent CH₃ and NO₂ groups, the facile transfer of a methyl hydrogen to oxygen followed by loss of an OH group gives rise to the m/z 210 ion which plays a key role in the six important fragmentation sequences that have been identified. A similarity of the reactions in the mass spectrometer to the decomposition pathways induced by other stimuli has been observed.     

Electron impact induced Balmer line emission from some aliphatic hydrocarbons

Absolute Balmer line emission cross sections are determined. The Balmer emission is obtained by dissociative electron excitation in propane, propylene and n-butane. The optical excitation functions measured for these lines are investigated in the medium energy range of 50–700 eV and normalized by a He bench-mark procedure. The measured data are corrected by an apparatus collection efficiency factor F to compensate for the loss of optical signal due to non-thermal energies of H-excited molecular fragments. The obtained results are determined with an accuracy of ± 15%. The absolute Balmer line cross sections are analysed according to the Bethe theory to get some information on primary excited parent molecular states. The power-law dependence for Balmer series has been determined.     

An investigation into the role of metastable argon atoms in the afterglow plasma of a low pressure discharge

An investigation into the behaviour of metastable argon atoms in a low pressure (250 Pa) pulsed electrical discharge was undertaken in an effort to find the cause of the persisting emission from sputtered metal atoms in the afterglow of an atomic fluorimeter. Results obtained by time-resolved emission and absorption measurements of several argon and copper spectral lines indicate that low energy electrons in the afterglow are converted to high energy electrons via the recombination of electrons with argon ions and the subsequent collisions of pairs of metastable argon atoms. The high energy electrons excite the sputtered metal atoms to give rise to a slow decaying emission tail in the afterglow. A probable change in the electron energy distribution in the afterglow may also have an effect on the observed emission. This phenomenon may be reduced by the use of a suitable quenching gas.     

The sublimation of argon, krypton, and xenon

In this paper, the sublimation pressure of Ar, Kr, and Xe are obtained as functions of temperature from an exactly integrated form of the Clapeyron equation. No fitting to experimental data of the equilibrium pressure has been necessary. The deviation plots of the sublimation pressure show that the results are satisfactory. The derived enthalpy of sublimation of the three rare gases from T = 0 K up to their respective triple point temperatures are asymmetric, distorted parabolas showing maxima for . The , which is a measure of the cohesion energy of the solid crystals, is easily calculated. A general equation has been obtained for as a function of temperature which also gives the enthalpies of sublimation of neon and radon. The (s + ? + g) triple point coordinates of Rn are reassessed.     

Light emission from chlorine atoms formed in the dissociative excitation of HCI in a flowing afterglow of discharged argon

Light emission from Cl(5p) atoms (near 440 nm) produced in the reaction of HCl in a discharged flow of argon was investigated with a flowing-afterglow apparatus. Ionic species, most probably argon ions in metastable states, Ar^+M, were found to be responsible for the Cl(5p) production in the dissociative excitation of HCl.     

Matrix isolation study of the products of the interaction of electrons and metastable argon atoms with HCCl2F

Two groups of infrared absorptions common to experiments in which samples of HCCl₂ isolated in an argon matrix at 14 K are exposed to vacuum ultraviolet radiation or to electrons produced by ultraviolet irradiation of an alkali metal, as well as to experiments in which the Ar:HCCl₂F sample is codeposited with a beam of argon atoms excited in a microwave discharge, have been assigned to anions produced upon associative and dissociative electron capture by HCCI₂F. Detailed isotopic substitution studies suggest that these anions are (Cl₂C)H?F^?, representing a unique type of hydrogen bonding, and HCCIF^?. The HCClF^? anion photodecomposes in the 345–250nm spectral region, but the products of its photodecomposition have not been identified. Both CCl₂ and Cl₂CF are also produced in the discharge experiments, but there is no evidence for the production of HCF. Mechanisms for the formation of ion products by electron capture and by exposure of HCCl₂F to radiation or to excited argon atoms of energy equal to or less than 11.8 eV are considered.     

Velocity dependence of vibrational branching ratios in electronic energy transfer collisions of metastable argon atoms with nitrogen

Measurements have been made of the vibrational branching ratio (υ′=0)/(υ′=1) in N^*₂ (C³Π_u) formed in electronic energy transfer collisions between argon metastable atoms and ground state nitrogen molecules, using crossed molecular beams. In the relative collision energy range, 0.08–0.20 eV, this ratio is 3.5±0.2.     

Photoelectron spectroscopy of naphthacene crystal in the vacuum ultraviolet region

The energy distribution curves of the photoelectrons emitted from naphthacene (C₁₈H₁₂) crystal in the vacuum ultraviolet region were measured by an ac modulated retarding potential method. The peaks in the curves, 5.8₃, 7.2₈, 8.2₉, 8.7₀ and 9.4₀ eV, are considered to be associated with the valence bands of the naphthacene crystal.     

Comparison in the analytical performance between krypton and argon glow discharge plasmas as the excitation source for atomic emission spectrometry

The emission characteristics of ionic lines of nickel, cobalt, and vanadium were investigated when argon or krypton was employed as the plasma gas in glow discharge optical emission spectrometry. A dc Grimm-style lamp was employed as the excitation source. Detection limits of the ionic lines in each iron-matrix alloy sample were compared between the krypton and the argon plasmas. Particular intense ionic lines were observed in the emission spectra as a function of the discharge gas (krypton or argon), such as the Co II 258.033 nm for krypton and the Co II 231.707 nm for argon. The explanation for this is that collisions with the plasma gases dominantly populate particular excited levels of cobalt ion, which can receive the internal energy from each gas ion selectively, for example, the 3d⁷4p ³G₅ (6.0201 eV) for krypton and the 3d⁷4p ³G₄ (8.0779 eV) for argon. In the determination of nickel as well as cobalt in iron-matrix samples, more sensitive ionic lines could be found in the krypton plasma rather than the argon plasma. Detection limits in the krypton plasma were 0.0039 mass% Ni for the Ni II 230.299-nm line and 0.002 mass% Co for the Co II 258.033-nm line. However, in the determination of vanadium, the argon plasma had better analytical performance, giving a detection limit of 0.0023 mass% V for the V II 309.310-nm line.     

TPEPICO studies near ionization threshold of argon and krypton clusters

Single photon ionization of argon and krypton clusters has been studied in the region between threshold and the ionization potential of the corresponding atom. Synchrotron radiation from the electron storage ring BESSY is used to ionize the clusters; threshold-photo-electron-photoion-coincidence (TPEPICO)-time-of-flight technique is used to detect ions correlated with the emission of zero-kinetic-energy-electrons. The spectra of the clusters in the range ofn=2 to 15 are discussed in view of the extensive fragmentation taking place in these systems. In order to characterize the properties of the clusters a method using scaling laws is applied. The principles and the deduction of Hagena's scaling parameter Γ* are briefly reviewed. Using Γ* an experimentally derived mean cluster size for molecular beams can be assigned. This allows one to clearly demonstrate the systematic variations of the measured spectra due to cluster fragmentation. As a general feature it is observed that, in the range studied, the peak in the measured ionization rate for a cluster ion (fragment) of a given size shifts to higher photon energies as the mean cluster size is increased.     

Photoionisation studies of homogeneous argon and krypton clusters using TPEPICO

The photoionisation threshold region of homogeneous Argon and Krypton clusters Ar _n and Kr _n forn up to 24 formed in a free jet expansion has been studied in detail, using the threshold photoelectron photoion coincidence (TPEPICO) time of flight technique. Measurements performed at a variety of different expansion conditions (nozzle temperature and stagnation pressure) demonstrate that fragmentation of larger clusters contributes substantially to the shape of the TPEPICO spectra even for the smallest clusters and at all photon energies higher than about 200 meV to 400 meV above the ionisation threshold. The determination of ionisation potentials for these cluster ions is discussed and careful estimates are given and compared with recent theoretical values.     

Photoelectron spectroscopy of naphthacene and perylene crystals by the rare gas emission lines

The energy distribution curves (EDC's) of the photoelectrons emitted from naphthacene (C₁₈H₁₂) and perylene (C₂₀H₁₂) crystals were measured using the rare gas resonance emission lines (He 21.22 eV, Ne 16.85 and 16.67 eV and Ar 11.83 and 11.62 eV). The peaks in the higher kinetic energy regions agree well with the peaks obtained from molecular photoelectron spectroscopy studies if constant energy shifts are assumed. In the lower kinetic energy regions, however, fixed kinetic energy peaks are found which are independent of the incident photon energies.     

The fusion curves of xenon,krypton, and argon

The experimental results on the fusion of the heavier rare gases at very high pressures, obtained in the last 20 years, are examined and analysed in conjunction with the measurements made at lower pressures from 1940 onwards. The parameters in the Simon equation for the melting curves of Xe, Kr, and Ar are determined, and the coordinates of a possible high-pressure {s(fcc) + s(hcp) + ?} triple-point are identified for each one of these three elements. The enthalpies of transition of the transformations involved are estimated as well as their respective values of the entropies of transition.     

The far from equilibrium structure of argon clusters doped with krypton or xenon

Heterogeneous clusters created by doping Ar host clusters with Kr or Xe are shown to have radically different structures from the mixed clusters of the same type created by co-expansion of Ar-Kr or Ar-Xe gas mixtures. In contrast to the co-expansion case, the doped mixed clusters can be produced with Kr or Xe on the surface and Ar in the bulk. With the doping technique it is thus possible to control the surface composition of a specific cluster. A study of the cluster properties as a function of the doping pressure is also reported for the case of Ar clusters doped with Xe. The clusters have been studied by means of synchrotron radiation based X-ray photoelectron spectroscopy.