A verification of the relativistic correction for electro-static electron spectrometers

The relativistic predictions for the non-linear calibration of a spherical sector electron spectrometer, operated with retardation in the constant δE/E mode, is verified to an accuracy of ± 0.05 eV over the energy range 0–2500 eV. The verification, involving the comparison of the energy deficit measured between the energy of peaks in the constant δE mode with that in the constant δE/E mode, is obtained by the use of an elastically reflected electron beam at 100 eV intervals over the full energy range. The energy deficit, for a VG Scientific ESCA 3 Mk II with a retard ratio of 1.656, increases from zero at 0 eV to 2.28 eV at 2500 eV. It is concluded that the spectrometer is very well behaved and that the established relativity theory is accurately verified in this investigation.     

Comment on a recent calculation of the Ham's reduction factors by the use of the exponential transformation method

The reduction factors p and q for an E electronic state with linear Jahn-Teller coupling to an E vibrational mode have been calculated numerically. The results together with other evidence suggest that the results obtained by Sigmund et al. using the transformation method are incorrect in the intermediate and strong coupling regimes.     

Quenching of the triplet state of Pd-porphyrins by Cu-etioporphyrin in dimethyl formamide

Quenching of phosphorescence of Pd-tetrabenzoporphyrin (Pd-TBP) and Pd-etioporphyrin I (Pd-EP) by the Cu-EP molecules was studied using pulsed photoexcitation. The rate constant of quenching (K _q) by the Cu-EP molecules was found to be 2.3×10⁹ 1/(mol s) for the low lying triplet state (TS) of Pd-Ep and 5.8×10⁸ 1/(mol s) for the TS of Pd-TBP. It is concluded that the quenching was caused by the intermolecular energy transfer, and the low value of K _q for Pd-TBP can be explained by the fact that the level of Cu-EP (X), to which the energy is transferred, lies above the TS of Pd-TBP (E _T=12 900 cm^?1). Based on the results obtained and the published data, it is assumed that the energy transfer proceeds via the formation of long-lived excited complexes of interacting molecules. With the K _q value for Pd-TBP and the results of kinetic analysis of the adopted quenching mechanism, the difference between the energy of states, involved in energy transfer, and the X state energy are determined (E _X=13 520 cm^?1 and E _T=14 500 cm^?1 for Cu-EP). Some specific features of photophysical and luminescence properties of Cu-porphyrins are explained by the presence of such a state related to the excitation of the copper ion.     

High spin states in the transitional nucleus88Mo

The reaction⁵⁸Ni(³⁶Ar,α qρ)⁸⁸Mo has been studied at 145 MeV beam energy. A detector array consisting of the OSIRIS spectrometer, four charged-particleΔE detectors and seven NE213 neutron detectors has been used to meaure the gamma radiation inγγ- and particle-γγ-coincidence mode. The level scheme of⁸⁸Mo has been extended up to 11.6 MeV excitation energy and probable spin 23?; some 70 transitions and 40 levels have been identified. Spin assignments have been proposed on the basis of measured DCO ratios. Hartree Fock cranking calculations of the Total Routhians and shell model calculations of the high spin states are presented which imply near-sphericity of the yrast line up to the highest spins found. A classification of the high spin states according to their leading seniority is proposed.     

Extrapolation from positive to negative energy of the Woods-Saxon parametrization of the n-208Pb mean field

The real part V(r); E) of the nucleon-nucleus mean field is assumed to have a Woods-Saxon shape, and accordingly to be fully specified by three quantities: the potential depth U_v(E), radius R_V(E) and diffuseness a_v(E). At a given nucleon energy E these parameters can be determined from three different radial moments [r^q]_v = (4π/A) ∝V(r; E)r^q dr. This is useful because a dispersion relation approach has recently been developed for extrapolating [r^q]_V(E) from positive to negative energy, using as inputs the radial moments of the real and imaginary parts of empirical optical-model potentials V(r; E) + iW(r; E). In the present work, the values of U_v(E), R_v(E) and a_v(E) are calculated in the case of neutrons in ²⁰⁸Pb in the energy domain −20 < E < 40 MeV from the values of [r^q]_V(E) for q = 0.8, 2 and 4. It is found that both U_V(E) and R_v(E) have a characteristic energy dependence. The energy dependence of the diffuseness a_a(E) is less reliably predicted by the method. The radius R_V(E) increases when E decreases from 40 to 5 MeV. This behaviour is in agreement with empirical evidence. In the energy domain −10 MeV < E < 0, R_V(E) is predicted to decrease with decreasing energy. The energy dependence of the root mean square radius is similar to that of R_V(E). The potential depth U_v slightly increases when E decreases from 40 to 15 MeV and slightly decreases between 10 and 5 MeV; it is consequently approximately constant in the energy domain 5 < E < 20 MeV, in keeping with empirical evidence. The depth U_v increases linearly with decreasing E in the domain −10 MeV < E < 0. These features are shown to persist when one modifies the detailed input of the calculation, namely the empirical values of [r^q]_v(E) for E > 0 and the parametrization [r_q]_w(E) of the energy dependence of the radial moments of the imaginary part of the empirical optical-model potentials. In the energy domain −10 MeV < E < 0, the calculated V(r; E) yields good agreement with the experimental single-particle energies; the model thus accurately predicts the shell-model potential (E < 0) from the extrapolation of the optical-model potential (E > 0). In the dispersion relation approach, the real part V(r; E) is the sum of a Hartree-Fock type contribution V_HF(r; E) and of a dispersive contribution ΔV(r; E). The latter is due to the excitation of the ²⁰⁸Pb core. The dispersion relation approach enables the calculation of the radial moment [r^q]_ΔV(E) from the parametrization [r^q]_w(E): several schematic models are considered which yield algebraic expressions for [r^q]_ΔV(E). The radial moments [r^q]_HF(E) are approximated by linear functions of E. When in addition, it is assumed that V_HF(r; E) has a Woods-Saxon radial shape, the energy dependence of its potential parameters (U_HF, R_HF, a_HF) can be calculated. Furthermore, the values of ΔV(r; E) can then be derived. It turns out that ΔV(r; E) is peaked at the nuclear surface near the Fermi energy and acquires a Woods-Saxon type shape when the energy increases, in keeping with previous qualitative estimates. It is responsible for the peculiar energy dependence of R_V(E) in the vicinity of the Fermi energy.     

Microwave spectrum and structure of methyl phosphonic difluoride

The rotational spectrum of methyl phosphonic difluoride has been reinvestigated using a pulsed-molecular-beam Fabry-Perot cavity microwave spectrometer. The enhanced resolution of the Fourier transform microwave (FTMW) spectrometer (compared to the original work done in a conventional Stark spectrometer) has allowed the measurement of small A-E splittings of many of the rotational transitions caused by the internal rotation of the methyl top. The barrier to internal rotation, V₃ = 676 (25) cm⁻¹, has been determined experimentally from the A-E splittings of the rotational transitions in the ground vibrational state. This barrier height is substantially lower than the previously determined value for the barrier, which was 1252 (14) cm⁻¹. High-level ab initio calculations at the MP2/aug-cc-pVTZ level predict a barrier to internal rotation of 638 cm⁻¹, in agreement with the experimentally determined value found here. The high sensitivity of the FTMW spectrometer has also permitted the measurement of the ¹³C and ¹⁸O isotopomers in natural abundance. The addition of these two isotopomers has allowed an improved structural determination.     

Model-independent analysis of the weak interaction in e− -N elastic scattering experiments

We discuss what model-independent information about the parity non-conserving electron-quark neutral current interaction can be obtained in the experiments on elastic scattering of longitudinally polarized electrons on unpolarized nucleons. Two possible forms of the neutron electric form factor G_E^γn(q²) are used in our analysis. The interpretation of the P-odd asymmetry, measured in these experiments, in terms of electron-quark neutral current coupling constants depends on the form chosen for G_E^γn(q²). We note also that the polarized e^?-p elastic scattering experiments might be used in principle to study the q² dependence of G_E^γn(q²).     

Nichtsenkrechte Interbandübergänge in Graphit durch unelastische Elektronenstreuung

Characteristic energy loss measurements are carried out on natural graphite single crystals. The frequency and wave vector dependent dielectric constant ?(ω,q) forq⊥c-axis is determined by Kramers Kronig Analysis. The results are interpreted in terms of non vertical interband transitionsE(k)→E(k+q) between the π-bands within the two dimensional approximation.     

Neutron spectrometer based on a proton telescope with electronic collimation of recoil protons

A prototype of a neutron spectrometer based on a gas proportional counter with recoil-proton registration is created at the Frank Laboratory of Neutron Physics at the Joint Institute for Nuclear Research (FLNP JINR) in Dubna. The spectrometer is developed to measure the kinetic energy of protons scattered elastically at small angles that are produced by (n, p) reaction in an environment containing hydrogen. The elaborated prototype consists of two cylindrical proportional counters used as cathodes. They are placed in a gas environment with a common centrally situated anode wire. Studies on the characteristics of the neutron spectrometer were conducted using ²⁵²Cf and ²³⁹Pu-Be radioisotope neutron sources. Measurements were made with monoenergetic neutrons produced by the ⁷Li(p, n)⁷Be reaction when a thin lithium target was bombarded with a proton beam from an EG-5 electrostatic accelerator, as well as with neutrons from the reaction D(d, n) ³He with a gas deuterium target.     

Electric monopole component in the 2+' → 2+ transition in 192Pt

Angular correlation measurements of K- and L-conversion electrons following the decay ¹⁹²Ir → ¹⁹²Pt have been made using a spectrometer with Ge(Li) and Si (Li) detectors. Absolute and relative internal conversion coefficients of transitions in ¹⁹²Pt were measured, using an ICC and prism β-spectrometers, to ≈ 2 % and values of δ_γ determined from the relative ICC. The experimental values measured in the study, A₂₂(K296γ316) = 0.138 ± 0.010, A₂₂(L296γ316) = 0.125 ± 0.013, α_K(296) = 0.0711 ± 0.0011, K/L_III = 9.65 ± 0.13. With δ_γ = + 5.4 ± 0.2, were employed for determining the E0/E2 amplitude ratios of conversion transitions, q(E0/E2), and the penetration parameter λ of the Ml component for the 2⁺' → 2⁺ (296 keV) transition in ¹⁹²Pt. The angular correlation measurements of L-conversion electrons enabled the elimination of one of two ranges of values of q and λ usually obtained. For the first time in our work, analysis of the e_Lγ angular correlation for the determination of the E0 component in the transition was carried out. As a result, q = +0.04 ± 0.05 with λ = ?4.5 ± 3.5 was obtained for the 296 keV transition. In this case, _ρ(E0) = 0.004 ± 0.005 agrees with _ρ(E0) = +0.006 determined theoretically by Kumar and Baranger for the 2⁺' → 2⁺ transition     

On the core electron binding energy of carbon and the effective charge of the carbon atom

From Mulliken population data based on ab initio calculations of a series of substituted aromatic compounds and from well-calibrated XPS data (core electron binding energies, E_b) an empirical relation between E_b(C1s) and the charge on the carbon atoms, q_c, has been found: E_b(C1s = 6.42q_c + 4.52q²_c + 285.8 (eV). It is also found that XPS data for other carbon-containing species, notably the cyanide ion, can be described by this relation.     

Empirical and theoretical investigation of the average potential of nucleons in 40Ca and 208Pb

From compilations of the empirical values of the complex mean field V(r; E) + iW(r; E) felt by protons and neutrons in ⁴⁰Ca and ²⁰⁸Pb, it is concluded that the radial moments ∫ V(r; E)r^q dr and ∫ W(r; E)r^q dr are fairly well determined by the experimental data, the favoured values of the exponent being q ≈ 0.4–0.8 in the case of the real part V and q≈ 1.2 ± 0.4 in the case of the imaginary part W. For a given value of q, the energy dependence of the radial moment of V can be obtained from that of W by means of a dispersion relation. The latter satisfactorily accounts for the anomalous energy dependence of the radial moments of V at low energy. It predicts that this anomaly is accompanied by a rapid energy dependence of the radial shape of V, in keeping with a recent phenomenological analysis of the scattering cross sections of neutrons by ²⁰⁸Pb.     

Some characteristics in the interaction of slow highly charged I ions with a Si(1 1 1) 1 × 1-H surface

We have observed secondary particles and photons emitted from hydrogen terminated Si(1 1 1) 1 × 1 surfaces in the interactions with highly charged ions (HCIs) of iodine having a wide range of charge state, q, from I¹⁷⁺ up to I⁵³⁺, fully stripped iodine ion. A TOF-SIMS (time-of-flight secondary ion mass spectrometry) apparatus has been used to investigate secondary emissions where protons are dominant signals in the TOF spectra. Measured yields of H⁺ and show strong q-dependences, proportional to q^3.4 and q⁵, respectively. For Si⁺, while the yield remains constant for q < ∼ 25, it begins increasing with q^1.4 at higher q (∼25). The mechanism of secondary emissions is briefly discussed.     

Elastic scattering of slow electrons by calcium atoms into an angular range depending on the collision energy

The use of trochoidal and hypocycloidal spectrometers that are applied in modern experimental techniques for studying processes of electron scattering by atoms, ions, and surfaces is considered in some detail. The angular range of the collection of scattered electrons is determined by the operation mode of the spectrometer and depends on the collision energy. To analyze the structure of the measured energy dependence S(E), an analytical formalism reflecting both resonance and nonresonance features of low-energy scattering was used. A theoretical analysis of elastic scattering of slow (to 2 eV) electrons by Ca atoms permitted the interpretation of the observed structure of S(E) as a manifestation of the ² D shape resonance. A comparison of the theoretical values of the S(E) function with the total and differential scattering cross sections was performed.     

The phonon spectra of trigonal selenium at 77 and 298°K

Phonon dispersion curves in the principal symmetry directions of trigonal selenium single crystals have been measured by neutron inelastic scattering, using a three-axis spectrometer. The acoustic modes and the three lowest-lying optical modes (q = 0 energy transfers of 13·5 and 18·5 meV) have been measured at 77°K. The acoustic modes have also been measured at 298°K. There are small frequency shifts between the two temperatures, but the general agreement between the acoustic mode frequencies measured at the two temperatures is excellent. The data have been fit by a force constant model which assumes completely general harmonic forces between the first two neighbors in the same covalently bonded chain and axially symmetric forces derived from a potential of the form V = ? Ar^?m + Br^?n between all other atoms out to an interatomic distance of 6·5 . Fits were carried out with (m; n) = (3; 5) and (6; 12). For the former, the best values of A and B correspond to a Van der Waals equilibrium distance of 3·9and a minimum energy at this distance of 1·5 × 10^?13 ergs (about 2 kcal/mol). There are, however, significant discrepancies between the calculated and observed dispersion curves which indicate that a more sophisticated force model is needed.     

In-beam spectroscopy of low energy conversion electrons with a recoil shadow method — A new possibility for subnanosecond lifetime measurements

An electron spectrometer consisting of an electron transport system with normal conducting solenoidal coils and a Si(Li)-detector as the energy dispersive element is described. It can be used for in beam spectroscopy of electrons in three different modes. The first one is the usual broad range mode with a low energy cut off of the transmission performed by a tantalum disk between target and detector. The second one is the lens spectrometer mode. An envelope baffle system permits electron detection in a momentum bandΔp/p=0.12. To cover a large energy range the magnet current is sweeped. In the third mode—the recoil shadow method — a longitudinal semicylindrical baffle between target and Si(Li)-detector allows spectroscopy of delayed electrons emitted from recoil nuclei in flight. Special features of this method are high transmission, and strong suppression of the promptδ-electron background. Lifetime measurements based on the detection of conversion electrons are possible by variation of the target position. This was tested with the¹⁵²Sm(¹⁶O,xn)^168?xYb compound nuclear reaction at a recoil velocityν _r=0.01 c, where half lives between 0.1 ns and 1 ns were determined.     

Interaction of low energy (5–10 keV) argon atoms and ions with a Cu(100) surface; Ion fraction,ionization and neutralization

The ion fractions η⁺ of low energy (5–10 keV) argon particles scattered from a Cu(100) surface, are measured with a time of flight spectrometer. Neutral as well as charged projectiles are used. The scattering angle θ is 30°. The results for different angles of incidence ψ and crystal directions are reported. For scattering in the 〈100〉 direction, with a ψ-value of 15° and a primary energy E₀ of 5 and 10 keV, the ion fractions for the quasi single scattering peak, η⁺_QS, are 1.5 and 6.1% respectively. When E₀ is between 5 and 10 keV a reionization process with a constant reionization probability occurs during the violent interaction. This process, but also neutralization along the outgoing trajectory, determines η⁺_QS. With ions as projectiles, an energy difference of about 16 eV is observed between the quasi single scattering peaks in the spectra of all scattered particles and of ions only. The ion fraction for the quasi double scattering peak, η⁺_QD. depends largely upon E₀, indicating that the efficiency of the reionization process increases with E₀. A qualitative discussion of the data is given, using the reionization process and the interatomic neutralization processes along the trajectory of the scattered particles.     

Inelastic electron scattering in nickel

Using a 200 keV electron spectrometer, with an energy resolution of ～0.25 eV and a momentum resolution of ～0.2 A^-1, we have measured the energy loss spectra for transmission of electrons through thin (～600 Å) Ni films. These results address the general question of the validity of momentum transfer estimates in electron loss scattering.Using low-energy electron backscattering, we have observed the dipole forbidden M₁ transition at 112 eV. For high-energy scattering, we have observed this transition only at high momentum transfer (q? 2 A^-1). These results indicates sizable contributions from high momentum transfer collisions in the low-energy experiments.     

An analytic calculation of the weak field limit of the static color dielectric constant

We analyze the Dyson equation/Ward identity system for the axial gauge n · A = 0 gluon propagator Δ_μν(q)whenn · q = 0. The solution behaves like (q^?4 + (q²)^ν?1) for small q₂, and we are able to calculate the power ν analytically. It turns out to be 0.1737. This analytic calculation verifies our earlier numerical solutions to these equations. For static problems, n · q = 0 is the temporal gauge, and in this gauge the gluon propagator is directly related to the color dielectric constant. We can thus calculate the dielectric constant in the infrared limit.