Ar 2s Research Articles

Energy analysis of ejected electrons in the region of the Ar L1-L2,3M Coster-Kronig transitions (25–56 eV) induced by electron impact

The ejected electron spectra between 25 and 56 eV kinetic energy in Ar have been measured at several electron impact energies. When the incident energy is above the Ar 2s ionization potential the peaks due to the L1-L2,3M1 and L1-L2,3M2,3 Coster-Kronig (CK) transitions are expected to occur in this region of kinetic energy, but we observe a series of other narrow structures that overlap and sometime dominate the spectrum due to the CK transitions. These features have been attributed to the autoionizing decay of inner valence doubly excited states to the Ar + ground state.

Role of cascade double Auger decay in the PCI distortion of the Ar 2s photoelectron line

We have investigated both experimentally and theoretically the post collision interaction effect on Argon 2s photoelectrons in the case of cascade double Auger decay. New features of this effect are revealed.

Post collision interaction probed by multi-electron coincidences: Application to the Ar 2s inner-shell photoionization

Post-collisional interaction following inner-shell ionization of atomic systems has been investigated by multi-coincidence electron spectroscopy, with a special emphasis on the decay by emission of two Auger electrons. The case of the Ar 2p hole is first reviewed. After Ar 2s inner-shell photoionization, the dominant decay channel is cascade Coster–Kronig/Auger decay. The distortion of the photoelectron peak shows a sensitivity to both the energy of the Coster–Kronig electron and to the lifetime of the intermediate Ar2+ (2p−13l−1) state that is well reproduced by a theoretical model based on the eikonal approach. The dynamics of cascade double Auger decay can be clearly understood thanks to this study.

Multi-electron spectroscopy: Auger decays of the argon 2s hole

Auger decay of an inner shell hole is an efficient way to create multiply charged ions in the gas phase. We illustrate this with the example of the argon 2s decay, and show that multi-electron coincidence spectroscopy between the 2s photoelectron and all released Auger electrons leads to a complete reconstruction of the Ar 2s decay cascade. Spectra of the intermediate and final Ar(n+) states are obtained and are compared with a theoretical model.

Trends in near-threshold photoionization of off-the-center endohedral atoms

Calculations of the photoelectron angular distribution from atoms confined in a fullerene cage have been performed using a recently developed theory of inner-shell near-threshold molecular photoionization. Trends uncovered in the modification of near-threshold photoelectron angular distribution of the A-C{sub 60} molecules as a function of the displacement of the confined atom from the center of the C{sub 60} cage are demonstrated. Specific results for Li 1s from Li-C{sub 60}, and Ar 1s, 2s, and 3s from Ar-C{sub 60} molecules are presented. In addition, the situation where the encapsulated atom lies in the vicinity of the center of one of the carbon hexagons of C{sub 60} and also when it is displaced beyond the fullerene cage, has been studied. It has been found that the photoelectron spectra are extremely sensitive, both qualitatively and quantitatively, to even a small displacement of the confined atom from the center of the cage. The existence of the C{sub 60} molecule even affects the atom's photoelectron angular distribution when it is a significant distance away.

Exploratory study of the reaction of bis(2-methoxyethyl)aminosulfur trifluoride (Deoxofluor™ reagent) with diaryl sulfoxides: novel routes to Ar 2SF 2 and Ar 2SF(OTf) via sulfoxide activation

Neither bis(2-methoxyethyl)aminosulfur trifluoride (Deoxofluor™ reagent) nor HF/pyridine alone can fluorinate diaryl sulfoxides. S-fluorination can be effected by activating the sulfoxide via protonation with HF/pyridine (70:30) to form sulfoxonium ions in equilibrium which are then S-fluorinated in situ with Deoxofluor™ to give Ar 2SF 2 compounds. Conversions depend strongly on steric factors and the reactions require the use of excess Deoxofluor™ and HF/pyridine. NMR data for the resulting diarylsulfur difluorides are gathered and discussed. Sulfoxide activation via diaryl (trifloxy) sulfonium triflate generated in situ from Ar 2SO with triflic anhydride at low temperature represents another strategy for S-fluorination with Deoxofluor™ to generate Ar 2S(OTf)F.

(e, 2e) cross sections for inner-shell ionization of argon and neon

Distorted-wave Born approximation (DWBA) calculations are reported for inner shell ionization of Ar(2p), Ar(2s) and Ne(1s) in the energy range 2-3 keV. Comparison is made with experimental data of Bickert et al. Agreement between DWBA and experiment is very good and much better than in previous comparisons with first Born type theories. The results show the importance of taking proper account of the strong static potential of a 'heavy' atom, particularly in inner shell ionization where the ionization process takes place in a region in which the static potential is at its strongest. Some interesting structures outside the angular range of the experimental data are revealed, these would be worthy of further experimental investigation. The electron momentdensity of the 2s orbital is measured for the first time and found to be in good agreement with the Hartree-Fock calculations of Clementi and Roetti (1974).

X alpha method with theoretically determined parameter alpha : calculation of shake-up and multi-electron X-ray transition energies

A method providing ab initio, self-consistent parameters alpha for the X alpha theory has been reviewed. Shake-up energies on the Ne 1s and Ar 2s and 2p levels have been determined by the Z alpha method with theoretical parameters alpha . A few RER (radiative electron rearrangement) transition energies for the elements N, Ne, K, Fe, Si, Ca and Ti are also presented.

Intramolecular sulphur(II)—oxygen interaction in sulphides and disulphides with 2-methoxycarbonylphenyl and 2-nitrophenyl groups: an X-ray study

The molecular structures of methyl 2-(methylthio)benzoate, dimethyl 2,2′-dithiodibenzoate, dimethyl 2,2′-thiodibenzoate, methyl 2-(2-nitrophenylthio)benzoate, 2,2′-dinitrodiphenyl sulphide and methyl 2-(2-nitrophenylthio)phenylacetate exhibiting S(II)⋯O(carbonyl) or S(II)⋯O—(nitro) close contact have been investigated by X-ray diffreaction. Planar (ArSMe), equatorial (Ar 2S 2) and skew (Ar 2S) conformations are explained by steric and conjugative effects and sulphur(II)—oxygen interaction. Linear and non-linear X—S⋯O close contacts resulting from favourable “bond direction” and unfavouralbe “lone-pair direction” approaches (2.619–2.722 and 2.900–3.402 Å, respectively) are discussed in detail. Possible aryl ring positions, the geometry of rings with S⋯O contact and the nature of counter-atom (X = C, S) are considered as decisive factors. The results are consistent with different neighbouring group effects found earlier for o-CO 2Me, o-CH 2CO 2Me and o-NO 2 groups. Data support the mutual dependence of S—S and S⋯O distances in compounds with a linear S—S⋯O arrangement. Other bond lenghts, e.g. CO, NO and S(II)—C ar are not affected significantly by sulphur—oxygen interaction.

“Increased-valence” structures and the bonding for some cyclic sulphur-nitrogen compounds

For the following (mostly cyclic) thiazyl compounds, attention is given to the construction and examination of “increased-valence” structures when sulphur 3 d-orbitals are omitted from the bonding schemes: S 4N 4 and its adducts, Ar 2S 4N 3 +, S 4N 3 +, S 4N 4O 2, S 4N 4 2+, S 5N 5 +, S 4N 5 −, S 4N 5O −, S 5N 6, S 3N 2 +, S 6N 4 2+, and S 3N 2X (with X  Cl +, NSO 2F, NCOCF 3, and NP 3N 3F 5). Lewis-Langmuir octet structures are written down, and then some of the non-bonding electrons for these structures are delocalized into bonding SN orbitals. The resulting “increased-valence” structures have one-electron-bonds and fractional electron-pair bonds, as well as normal electron-pair bonds. The hypothesis that fractional electron-pair bonds are shorter than one-electron bonds leads to deductions concerning the relative lengths of the SN bonds that are mostly in general agreement with the experimental values. The nearest-neighbour SS bonds for each of S 4N 4, S 4N 5 −, S 5N 6 S 4N 3 +, S 3N 2 + and derivatives, and S 6N 4 2+ are longer than the standard SS single-bond length of ∼ 2.06Å. These lengthenings are due either to less-than-unity values for the SS σ-bond numbers in the “increased-valence” structures, or to the straining of the SS σ-bonds as a consequence of local planarity requirements. The results of simple Hückel molecular orbital calculations of bond lengths are also reported for some of the planar systems. The calculations support the hypothesis that expanded valence-shell linkages (such as ▪ and ▪ for 2-and 3-coordinate sulphur) are not required in the valence structures for the systems considered in this paper.