Measurements of circular polarization correlations following excitation of Ar and Kr by electron impact

We report measurements of the circular polarization correlation parameterP ₃ for the excitation of the 4s′[1/2] _j=1 state in Ar by 40 eV electrons and for the excitation of the Kr 5s[3/2] _J=1 state by 30 eV electrons at electron scattering angles up to 50°. The measured Ar data are compared to predictions of a distorted wave Born approximation (DWBA). The agreement is in general not very good with theory predictingP ₃ values considerably larger than the measured values in the regime of small scattering angles. In Kr, where the measured data are compared to theoretical predictions from a DWBA, a first-order many-body theory (FOMBT) and a relativistic distorted wave theory (RDW), the level of agreement between experiment and theory is somewhat better. The measuredP ₃ parameters in conjunction with the previously measured linear coherence parametersP ₁ undP ₂ under the same scattering conditions yield the total polarizationP _tot ⁺ which is a measure for the level of coherence in the excitation process. In both cases studied here, we found values of eliminateP _tot ⁺ that were consistent with a fully coherent excitation process.     

On the energy difference between the lP and 3P states of the beryllium isoelectronic sequence

Wave functions of the ¹S (ground state), ³P and ¹P states for the beryllium isoelectronic sequence have been obtained in various approximations. The HF ²p orbitals for the ¹P and ³P states are similar except for Be, where the ²p orbital is quite diffuse for the ¹P state. The difference between the experimental E(¹P) – E(³P) and the HF E(¹P) – E(³P) is 0.62 eV for Be and 1.17 ～ 1.40 eV for B⁺ ～ F⁵⁺. The disagreements are attributed to the correlation effects between the 2s and 2p electrons. This is confirmed by ci calculations. It is shown that a limited basis SCF calculation reproduces the above feature of the HF results if we treat the orbital exponents as the variational parameters. The use of the Slater values for the orbital exponents is shown to be inadequate especially for the Be ¹P state. The conclusions of this paper will be useful for discussing the V–T separations of H₂ and C₂H₄.     

The yields of1 P and1 D resonances in the He(e, 2e)He+ reaction

In the first Born approximation the dependence of the yields of the¹ P and¹ D resonances in the He(e, 2e)He⁺ reaction on the momentum transfer in the recoil peak region at incident energiesE ₀=1000 eV is studied. It is shown that in a certain range of the ejection angle and for the large momentum transfer the yield of the¹ D resonance dominates over the¹ P resonance one.     

Ground state correlation energy of the Be-sequence forZ=4–20 in MCDF approximation

The ground state (J=0) electronic correlation energy of the 4-electron Be-sequence is calculated in the Multi-Configuration Dirac-Fock approximation forZ=4–20. The 4 electrons were distributed over the configurations arising from the 1s, 2s, 2p, 3s, 3p and 3d orbitals. Theoretical values obtained here are in good agreement with experimental correlation energies.     

Electron-impact coherence parameters for the excitation of the 51 P state of Sr

Electron-photon polarization correlation measurements have been carried out for the excitation of the 5¹P state of Sr at electron impact energies of 30.3 and 58.4 eV and electron scattering angles of 20°–130° for 30.3 eV and 20°–100° for 58.4 eV. The resulting Stokes parametersP ₁,P ₂,P ₃ are used to derive the usual complete scattering parameter sets λ, χ and γ,L _⊥,P _l. New FOMBT calculations for these parameters are reported alongside the measured data and show substantial agreement with the experiment and with recent calculations by Srivastava et al.     

Resonances in helium atoms associated with theN=4 andN=5 He+ thresholds

Some doubly excited autoionising states of helium atoms converging on theN=4 andN=5 He⁺ thresholds are calculated by use of a method of complex-coordinates. States withL≧2 and with parities of (?1) ^L and (?1) ^L+1 are calculated by using products of Slater-orbital type wave functions with expansion lengths up to 319 terms. Resonance parameters (both resonance energy and autoinoisation width) are calculated for states with angular momentum up toL=7 forN=4 resonances, andL=8 forN=5 resonances.     

Alignment of Ar+ (2p −1 2 P 3/2) ions after electron impact ionisation in the range 1 keV to 268 eV

We have measured the alignmentA ₂₀ of Ar⁺(2p ^{?1 2} P _3/2) ions after electron impact ionization in the range of primary electron energyE ₀=1000...268 eV (range of excess energyE ₁=750...19.5 eV) via the anisotropic angular distribution ofL ₃?M _2,3 M _2,3(¹ S ₀) Auger electrons. On decomposing the Auger spectra into their components special care was taken by including the effect of the postcollision interaction on the shape of Auger lines. The present alignment values forE ₀≧350 eV agree well with previously existing experimental values of DuBois and Rodbro and with theoretical DWBA results of Berezkho and Kabachnik, but forE ₀<350 eV they deviate systematically from the DWBA values. For the lowest impact energyE ₀, which is only 19.5 eV above threshold, we obtainedA ₂₀=+0.09(16). This value clearly indicates that in the ionisation process near threshold the two low-energy electrons escape not only with a two-electron partial waveL=0, according to Wannier's original assumption, but also with partial wavesL>0.     

Electron-impact excitation of the transition 1s 22s 22p 5(2 P 3 2/0 −2 P 1 2/0 ) of Mg IV

Effective collision strengths for electron-impact excitation of the ground state fine structure transition² P ₃ ^2/0 ?² P ₁ ^2/0 have been calculated by using theR-matrix method. Twelve lowest target states, represented by configuration interaction wavefunctions are included in the scattering calculations.M1 andE2 transition probabilities are also calculated by employing the Breit-Pauli Hamiltonian.     

High resolution electron momentum spectroscopy of the valence orbitals of water

The development of a third-generation electron momentum spectrometer with significantly improved energy and momentum resolutions at Tsinghua University (ΔE = 0.45–0.68 eV, Δθ = ±0.53° and Δ? = ±0.84°) has enabled a reinvestigation of the valence orbital electron momentum distributions of H₂O with improved statistical accuracy. The measurements have been conducted at impact energies of 1200 eV and 2400 eV in order to check the validity of the plane wave impulse approximation. The obtained ionization spectra and electron momentum distributions have been compared with the results of computations carried out with Hartree Fock [HF] theory, density functional theory in conjunction with the standard B3LYP functional, one-particle Green’s function [1p-GF] theory along with the third-order algebraic diagrammatic construction scheme [ADC(3)], symmetry adapted cluster configuration interaction [SAC-CI] theory, and a variety of multi-reference [MR-SDCI, MR-RSPT2, MR-RSPT3] theories. The influence of the basis set on the computed momentum distributions has been investigated further, using a variety of basis sets ranging from 6-31G to the almost complete d-aug-cc-pV6Z basis set. A main issue in the present work pertains to a shake-up band of very weak intensity at 27.1 eV, of which the related momentum distribution was analyzed for the first time. The experimental evidences and the most thorough theoretical calculations demonstrate that this band borrows its ionization intensity from the 2a₁ orbital.     

The effect of the electron spin on angular momentum transfer in Na*(32 P 3/2)+Na+ collisions — crossed beam experiment and semiclassical calculation

The angular momentum transfer between electronic and heavy particle motion has been studied for inelastic collisions of laser state-prepared Na*(3² P _3/2,M _J ) with Na⁺ leading to Na*(3² D) or Na(3² S) in the energy rangeE _cm=5?47.5 eV. The measurements are compared to semiclassical calculations employing the coupled channel method in the impact parameter approximation but including dynamics of the electron spin coupling to the heavy particle motion.     

Steps toward a high precision evaluation of the hyperfine interactions in neutral muonic helium

The solution of the Schrödinger equation of the neutral muonic helium is sketched by an eigenfunction expansion method: the eigenfunctions of the two Coulombic centres problem (of chargesZ ₁=2,Z ₂=–1) are used to expand the wave function. Our Born expansion method is a generalization of the Born-Oppenheimer approximation to a system in which the two centres (He, ^–) do not have a stable equilibrium distance. The adiabatic approximation is solved, upper-lower bounds on the eigenvalue are given for a number of states. The hyperfine energy corrections are calculated in general terms and are given numerically for the ground state and for the first muonically and electronically excited states in the frames of the adiabatic approximation. Our best value fails to give the observed hyperfine splitting of the ground state by some 5 × 10^–4 (2 MHz).     

Quantum-Chemical Modeling of the Effect of a Continuous Random Network on Stabilization of Charged and Neutral Defects in a-S

Quantum-chemical modeling of the stabilization of neutral and charged defects in amorphous sulfur (a-S) has been carried out. The atoms constituting the three nearest coordination spheres of a defect were modeled using the cluster approximation at the HF/6-31G* level. The interaction of the defect region with distant fragments of a continuous random network was calculated using the polarizable continuum model (PCM), in which the medium surrounding the cluster was considered as a continuum with the experimental permittivity for a-S. The energy of formation of charged defects E _def based on threefold coordinated sulfur atoms (C ₃ ⁺ , ₃ ^? )is close to the homolytic bond cleavage energy E _b. For neutral defects, E _def < E _b. Such defects can be the sites with a negative correlation energy, which are responsible for specific properties of chalcogenide glassy semiconductors.     

A direct test of the vibrationally adiabatic theory of chemical reactions

The adiabaticity assumption of the vibrationally adiabatic theory of chemical reactions in the zero-curvature approximation is directly tested for the collinear H + H₂ reaction against calculations using exact wavefunctions. It is found that the symmetric stretch motion of the transition state is adiabatic to within 10% for total energies E ranging from 0.51 eV to 0.72 eV. For E below the zero-point energy of this symmetric stretch motion non-adiabaticity is substantial and is probably due to tunneling. For E above the first excited vibrational state energy of this symmetric stretch motion the adiabaticity assumption breaks down completely.     

Spin exchange in low energy electron-ion collisions

The elastic scattering of an electron by a hydrogenic ion of charge (Z-1) is investigated. For scattering energiesE _kin in the eV region, where the Bohr-Sommerfeld parametery is large compared to one, the cross section for spin exchange of the electrons is found to be proportional toZ ^?2 andE ^?1 _kin. Spin exchange is dominated by radiative electron capture forZ>25.     

Laser fluorescence studies of HF rotational relaxation

Rotation relaxation of HF in HF-Ar mixtures was observed using a laser infrared fluorescence technique. A specific vibrational-rotational state of HF was excited, and the fluorescence from HF was monitored. Total rotational energy-transfer rates, and individual state-to-state transition probabilities were obtained for υ = 1, J = 3 (ΔJ = ± 1, ±2) and υ = 1, J = 5; (ΔJ= ±1, ?2, ?3). The transition probabilities decreased with increasing ΔE_J,J, the energy transferred from R → T (rotation to translation). The data were fitted to a simple exponential model k_JJ, α exp(-ClΔE_J,J'l). C was estimated to be 1.55 ± 0.25 kcal^?1 mole.     

Temperature dependence of the volumetric properties of some alkoxypropanols + n-alkanol mixtures

The excess molar volumes V_m^E for binary liquid mixtures containing dipropylene glycol monomethyl ether or dipropylene glycol monobutyl ether and methanol, 1-propanol, 1-pentanol and 1-heptanol have been measured as a function of composition using a continuous dilution dilatometer at T=(288.15, 298.15, and 308.15) K and atmospheric pressure over the whole concentration range. The excess volume results allowed the following mixing quantities to be reported in all range of concentrations or at equimolar concentrations: α, volume expansivity; (∂V_m^E/∂T)_p; (∂H^E/∂P)_T at T=298.15 K. The obtained results have been compared at T=298.15 K with the calculated values by using the Flory theory of liquid mixtures. The theory predicts the α, and α^E values rather well, while the calculated values of (∂V_m^E/∂T)_p and (∂H^E/∂P)_T show general variation with the alkyl chain length of the alkoxypropanols. The results are discussed in terms of order or disorder creation.     

The Conductance- and Capacitance-Frequency Characteristics of the Rectifying Junctions Formed by Sublimation of Organic Pyronine-B on p-Type Silicon

The rectifying junction characteristics of the organic compound pyronine-B film on a p-type Si substrate has been studied. The pyronine-B has been sublimed on the top of p-Si surface. The barrier height and ideality factor values of 0.79±0.04 and 1.13±0.06 eV for this structure have been obtained from the forward bias current-voltage (I-V) characteristics. From the low capacitance-frequency (C-f) characteristics as well as conductance-frequency (G-f) characteristics, the energy distribution of the interface states and their relaxation time have been determined in the energy range of (0.53−E_v)-(0.79−E_v) eV taking into account the forward bias I-V data. The interface state density N_ss ranges from 4.93×10¹⁰ cm⁻² eV⁻¹ in (0.79−E_v) eV to 3.67×10¹³ cm⁻² eV⁻¹ in (0.53−E_v) eV. Furthermore, the relaxation ranges from 3.80×10⁻³ s in (0.53−E_v) eV to 4.21×10⁻⁴ s in (0.79−E_v) eV. It has been seen that the interface state density has an exponential rise with bias from the midgap towards the top of the valence band. The relaxation time shows a slow exponential rise with bias from the top of the valence band towards the midgap.     

Microwave spectrum of P14N and P15N: Spectroscopic constants and molecular structure

In the present work the J+1←J, with J=1–3, 6, 7, 10–16, rotational transitions of P¹⁴N and the J+1←J, with J=1, 2, 7, 8, 10–14, rotational transitions of P¹⁵N have been observed in the millimeter- and submillimeter-wave region. These measurements allowed us to improve the ground state rotational parameters of P¹⁴N as well as provide those of P¹⁵N for the first time. The present measurements have been combined with rotational and vibrorotational transitions available in the literature to yield the Dunham coefficients. The equilibrium structure has also been determined to a high accuracy. The experimental investigation has been supported by highly accurate ab initio computations.