Ar 3P2 Research Articles

Single ionization of Ar(2p) by antiproton and electron impact

Doubly differential cross-sections for ionization of Ar(2p) are presented within the framework of a three-body classical trajectory Monte Carlo method and the continuum-distorted-wave approximation. As a projectile we consider an antiproton with an energy of 3.67 MeV. We also present classical cross-sections for 2 keV electron impact where the electron velocity is equal to that of the investigated antiproton velocity. We show analogy between the cross-sections calculated by antiproton and electron impact.

Spectroscopic observation of electronically excited SO (A″ 3Σ +)

The radiation produced in an afterglow due to the reaction of Ar( 3P 0, 2 ) with SO 2 has been studied between 230 and 600 nm. Two progressions are assigned to SO species. Aside from SO (c 1Σ − → X 3Σ −), a new SO emission band located closely to the peak lines of SO (c 1Σ − → X 3Σ −) in the range of 400 and 600 nm was also discovered and assigned to the SO (A″ 3Σ + → X 3Σ −) transition. A set of spectroscopic constants for the A″ 3Σ + state was deduced as T 00 = 30 460 ± 18.0 cm −1, ω e ′ = 685 ± 8.0 cm − 1 , ω e ′ χ e ′ = 7.7 ± 0.8 cm − 1 .

Polarization effect in (e, 2e) collisions of argon

Calculations of the triple differential cross section (TDCS) for electron impact ionization of the Ar(2p) orbital in a highly asymmetric geometry, using modified distorted wave Born approximation (DWBA) methods, are reported. The role of the polarization effect in (e, 2e) collisions of Ar(2p) is considered in the calculations, and the calculated results shows that the polarization potential is particularly important.

Accurate calculation of core-electron binding energies: multireference perturbation treatment.

Multireference perturbation theory (MRPT) with multiconfigurational self-consistent field (MCSCF) reference functions is applied to the calculations of core-electron binding energies (CEBEs) of atoms and molecules. Orbital relaxations in a core-ionized state and electron correlation are both taken into account in a conventional MCSCF-MRPT procedure. In the MCSCF calculation, the target core ionized state is directly optimized as an excited state and this treatment can completely prevent a variational collapse. Multireference Moller-Plesset perturbation theory and multiconfigurational self-consistent field reference quasidegenerated perturbation theory were used to treat electron correlation. The present method quite accurately reproduced the 1s CEBEs of CH4, NH3, H2O, and FH; the average deviation from the experimental data is 0.11 eV using Ahlrichs' VTZ basis set. The C 1s and O 1s CEBEs of formic acid and acetic acid were calculated and the results are consistent with the bonding characters of the atoms in these molecules. The present procedure can also be applied to CEBEs of higher angular momentum orbitals by including spin-orbit coupling. The calculated CEBEs of Ar 2p, HCl 2p, Kr 3d, and HBr 3d are in reasonable agreement with the available experimental values. In the calculation of the 3d CEBEs, a relativistic correction significantly improves the agreements. The effect of polarization functions is also discussed.

Electron–electron coincidence study of double Auger processes in atoms

The double Auger process after Ar 2p and Ne 1s inner-shell photoionization is investigated by means of angle resolved time-of-flight electron–electron coincidence spectroscopy. This method allows to disentangle direct double Auger from cascade Auger processes. Information about the energy sharing as well as the angular correlation of the two emitted electrons is obtained. Circular dichroism in the double Auger emission produced by circularly polarized light is discussed.

Ar 2p excited states of argon in non-polar media

Ar 2p photoabsorption spectra for Ar solid and Ar mixture with Kr, Xe and N 2 have been measured in order to study Ar 2p excited states in solid phase. Based on difference between partial electron yield and fluorescence yield spectra for solid Ar, Ar 2p 3/2–4s and 2p 3/2–4p excitations on surface are identified. For Ar:Kr and Ar:Xe mixtures, all bands move to lower energy as the Ar concentration decreases. Compared with solid Ar, Ar:N 2 mixtures show small red shift for the Ar 2p 3/2–4s excitation and blue shift for broad bands originating from Ar 2p– nd excitations. The spectral differences between the mixtures are discussed in terms of the polarization stabilization of the ionization threshold and the exchange repulsion of the Rydberg electron by the valence electrons of the neighboring atoms/molecules.

Argon nanobubbles in Al(111): a photoemission study.

Two fundamental manifestations of Al conduction electron response to Ar atom core hole in the final state of photoemission have been studied in implanted Ar bubbles in Al(111). Ar 2p binding energy and the Doniach-Sunjić asymmetry of the core-level line shape vary systematically as functions of Ar+ implantation energy and number of ions bombarded (fluence). The observations are explained by relating the strength of Al conduction electron screening to the size of the Ar nanobubbles.

Theoretical and Experimental Study of the Angular Correlations in Auger Cascades in Noble Gas Atoms

An overview of recent experimental and theoretical studies of angular correlations in cascades of Auger transitions photoinduced in rare-gas atoms is given. In particular, the resonant Auger transitions from the photoexcited Ne 1s−13p, Ar 2p−14s, Kr 3d−15p, and Xe 4d−16p states to the states of ns−2n'l' and ns−1np−1n'l' configurations with a following Auger (Coster–Kronig) transition have been studied by means of angle-resolved electron spectroscopy including coincidence measurements of two emitted electrons. A theoretical interpretation of experimental results is given in the framework of the MCDF approach. In general the multi-configuration calculations agree very well with experiment.

Potential energy curves of diatomic molecular ions from high-resolution photoelectron spectroscopy. I. The first six electronic states of Ar2+.

High-resolution photoelectron spectroscopic data have been used to determine the potential energy curves of the first six electronic states of Ar2+. The potential energy functions properly include the effects of the long-range interactions and of the spin-orbit interaction and are of spectroscopic accuracy (1-2 cm(-1)) over a wide range of internuclear distances. The total number of adjustable parameters could be reduced to only 12 by truncating the long-range interaction series after the R(-6) term and assuming an R-independent spin-orbit coupling constant. This assumption was verified to be valid to an accuracy of +/-2 cm(-1) over the range of internuclear distances between 3.0 and 4.6 A. The interaction potential proposed by Siska [P. E. Siska, J. Chem. Phys. 85, 7497 (1986)] was generalized to a form that is expected to be sufficiently flexible to describe chemical bonding in other diatomic molecular ions. The potential energy curves are more accurate than the best available ab initio curves by two orders of magnitude and provide quantitative information on dissociation energies and equilibrium internuclear distances. The local maximum between the two potential wells of the I(1/2g) state was determined to lie 62 cm(-1) below the Ar(1S0)+Ar(+)(2P(3/2)) dissociation limit, and the II(1/2g) state is found to be significantly more bound (De=177 cm(-1)) than previously assumed.

Probing branching mechanism through resonance-type oscillation in the collision-energy dependence of Penning ionization reaction of Ar (3P) with oriented CH3I

The collision energy and orientation-angle-resolved Penning ionization cross sections were determined for the Ar (3P)+CH3I reaction. A remarkable depletion was recognized in the collision- energy dependence of the orientation-angle-resolved Penning ionization cross section. The depletion could be interpreted as the competitive neutral dissociation from the Rydberg states formed by an electron exchange mechanism related to a 3a1 molecular orbital. The stereo selectivity for the Penning ionization and neutral dissociation were discussed. From the series of our studies on Ar (3P)+CH3X (X=Cl,Br,I) reactions, it was substantiated that the orientation angle and collision-energy-resolved Penning ionization cross section give an important information about the branching mechanism to the Rydberg states that are linked to the neutral dissociation channels.

Effect of stress-induced phase transformation on nanomechanical properties of sputtered amorphous carbon films

The nanomechanical properties of radio-frequency sputtered ultrathin carbon films measured by surface force microscopy were correlated to the carbon bonding structures analyzed by x-ray photoelectron and Auger electron spectroscopy. The films consisted of amorphous carbon (a-C) comprising both trigonal (sp2) and tetrahedral (sp3) carbon hybridizations. The sp3 carbon content in the a-C materials of films with nanohardness of 19–40 GPa was found to be in the range of 22%–28%. From variations of the binding energy of Ar 2p electrons and the sp3 carbon content with the film Ar content, a stress-induced phase transformation from sp2 to sp3 carbon was determined at compressive residual stress of about 14 GPa. Film hardening occurs due to material densification, which is controlled by the intensity of the energetic Ar+ bombardment and the flux ratio of incoming C atoms and Ar+ ions during film growth. The results of this study elucidate the underlying hardening mechanism in ultrathin sputter-deposited carbon films.

Scanning tunneling microscopy images of argon monolayer on a monolayer graphite surface

We apply first-principles total-energy electronic structure calculations within the density functional theory (DFT) in the local density approximation (LDA) to calculate the scanning tunneling microscopy (STM) images of argon monolayer adsorbed on a monolayer graphite surface. The results are consistent with the experiments. It is demonstrated that the hybridization of C 2p electronic states (π-electronic states) with Ar 3p and 4s electronic states is the main origin of the Fermi-level local density of state (LDOS), which makes Ar atoms visible in the STM experiment.

Steric effect in the endothermic Penning ionization reaction of tert-butyl bromide with Kr(3P)

The steric opacity function (the dependence of reaction cross section upon mutual molecular orientation) for the endothermic Penning ionization channel of Kr(3P)+(CH3)3CBr reaction was determined by using an oriented tert-butyl bromide molecular beam at 0.1 eV average collision energy. A remarkably large steric effect was observed in contrast with the Ar(3P)+CH3Br reaction. We find that the ionization cross section is maximum at sideways and it becomes “zero” at the tert-butyl end. The Br end is found to be unfavorable as compared with sideways approaches. The stereo selectivity observed in the present work is discussed in terms of the electron exchange mechanism, in which the shielding effect by bulky nonreactive tert-butyl group as well as the smearing effect in impact parameter are taken into account.

Nuclear-excited Feshbach resonance in the Ar(3P)+CH3Br Penning ionization reaction under orientation and velocity specified collisions

The collision-energy and orientation-angle-resolved Penning ionization cross section was determined for the Ar(3P)+CH3Br reaction by using an oriented beam and a time-of-flight measurement. A remarkable resonance-type structure in the Penning ionization cross section is recognized in the collision energy dependence at fixed molecular orientations, which is very similar to the one we previously observed in the Ar(3P)+CH3Cl reaction. This resonance-type structure could be interpreted as a new type nuclear-excited Feshbach resonance where the branching to competitive neutral dissociation channel is enhanced due to the formation of vibrationally excited CH3Br Rydberg states.

Wave driven molecular discharges as sources of active species

Microwave N 2, H 2, N 2–Ar discharges driven by travelling surface waves are investigated as sources of active species [N( 4S), H(1s), N 2(A 3Σ u +),Ar( 3P 2)]. By means of optical emission and absorption spectroscopy, the population density of the species of interest has been detected. The results are discussed in the framework of self-consistent models. The correlation between wall conditions and volume density of H(1s) atoms and H − negative ions in H 2 discharge is pointed out.

Selective probing of the electronic structure of free clusters using resonant core-level spectroscopy

In this paper the first resonant photoemission and partial electron yield studies of free clusters are presented. The resonant photoemission spectra of free argon clusters have been recorded with excitation energies determined from the cluster X-ray absorption spectrum near the Ar 2p ionization threshold. The decay of 2p(-1)4s and 2p(-1)3d cluster surface and excited states has been investigated in detail. The combination of resonant photoemission and partial electron yield methods has allowed a selective probing of the electronic and geometric structure, yielding new results concerning the interplay between the energy of the excited states, their orbital character and the local atomic coordination. These new results demonstrate the power of resonant core level spectroscopy when applied to free clusters, as well as the advantages of free clusters for the studies of the bulk and surface energetics of nanoscale solids. (C) 2002 Elsevier Science B.V. All rights reserved. (Less)

Resonance enhanced deactivation of argon 4p'[1/2]o state by atomic oxygen and its impact on actinometry

Ar emission at 750 nm is often used in actinometry of reacting species in materials processing discharges. The upper excited state, 4p'[1/2]o(2p1), of this Ar emission line is nearly iso-energetic with three excited states of atomic oxygen that lie just below the O atom ionization limit. We have measured the resonant deactivation of this Ar excited state by O atoms in SF6/Ar/O2 rf-driven discharges with high O2 dissociation fractions. At fixed pressure and input power, the Ar emission at 750 nm decreases with O2 additions up to 10%. In marked contrast, emissions from Ar* states that lie above the O atom ionization limit either increase with O2 addition or do not change. In particular, strong emission from a 6s state at 641 nm increases linearly with O2 addition. Under these same conditions, emission of the 704 nm F atom line increases with O2 addition. Behaviour of the 750 nm emitting Ar 2p1 state is consistent with the other 4p (2pn) states each of which lies below the O atom ionization limit. All of the 4p (2pn) Ar excited states are nearly iso-energetic with high-lying atomic oxygen states. The energy defects are less than the available thermal energy in the discharge environment of this study. Each of the Ar 4p (2pn) states exhibit behaviour consistent with resonant O atom quenching.

THE SHAPES OF PHOTOELECTRON SATELLITE SPECTRA

Line shapes of photoionization satellites are theoretically investigated. Calculations were carried out for the satellite states 1s2s(3S)3s(2S) and 3s3p5(1P)4s(2P) of Ne 1s and Ar 3p vacancies, respectively, created in photoionization. Theory excellently reproduces experimental line shape parameters of the first satellite and predicts the two-peak structure of the second.

(e,2e)triple-differential cross sections of helium and argon at 64.6 eV

The distorted-wave Born approximation with spin averaged static exchange potential and modified semiclassical exchange potential has been used to calculate the triple-differential cross section of He (1s 2 ) and Ar (3p 6 ) in the coplanar to perpendicular plane geometry. Similar to helium a strong interference minima in the cross section has been observed for the argon atom for all the incident electron angles. The triple-differential cross section in the case of argon at low- and high-scattering angles is in very good agreement with the present experiment. Inclusion of postcollision interaction gives a dip at 45° (characteristic feature of p-orbital targets), which has not been observed exactly at 45° by the experiment and calculations without postcollision interaction. The agreement with experiment in case of helium is quite good, but in the case of argon, some discrepancies are still there.

ELECTRONIC ENERGY DISSIPATION PROCESSES IN DOPED RARE GAS CLUSTERS WITH A SHELL-LIKE STRUCTURE

Energy relaxation processes of photoexcited Ar M clusters (M < 50) covered with a shell of Kr atoms (up to 30 atoms) which are embedded in large Ne N clusters (N = 3500) are investigated with energy-resolved fluorescence spectroscopy. In the energy range of the Ne cluster absorption (16.5–18 eV) a strong energy transfer to the embedded Ar subcluster is observed, which results in desorption of electronically excited Ar * atoms. Ar * move through the Ne cluster, desorb and emit visible and near-infrared light in the vacuum ( 4p → 4s ). By coating the Ar clusters with Kr atoms, the Ar lines disappear and 5p → 5s transitions of Kr become dominant. Additionally, new bands occur, which are assigned to transitions of perturbed atomic Ar 4p states inside Ne clusters. A simple kinematic model is suggested to describe the suppression of desorption of excited Ar atoms from Ne clusters.