Self-consistent calculation of 1s2s1S state wave function of helium

A simple self consistent variation perturbation method in the coupled Hartree–Fock scheme has been proposed to calculate 1s2s ¹S state of the He atom. The present paper deals with an 1s2s ¹S wave function in which all the relevant orthogonality conditions are imposed in successive stages. The resulting wave functions together with some interesting features are discussed.     

Triple-differential cross sections of helium for (e, 2e) processes

The triple differential cross sections for electron impact ionization of helium in a symmetric coplanar energy-sharing geometry at incident energies from 45–500 eV and an angle of 45° are calculated by use of the modified BBK model. A comparison with other theoretical results has been performed. It has been found that the present results give an excellent agreement with the absolute experimental measurement for the energy range considered.     

Absolute triple differential cross sections for helium at 300 eV

Absolute triple differential cross sections for the ionisation of He by electrons with energies near 300 eV have been measured in asymmetric conditions. The kinematics of the experiment select ionising events which belong to the intermediate regime of energy and momentum transfer. The experiments are compared with the distorted wave Born approximation.     

Calculation of cross sections for penning ionization: He(2S,2S) + H(1S)

Cross sections for ionization of hydrogen atoms by metastable helium atoms are calculated using the best published values for the complex potential. The present cross section for the singlet metastable is quite different from previous determinations. The validity of the JWKB approximation has been verified.     

Self-consistent calculation of 1s2s3S state of helium and heliumlike ions

In this paper we present a simple method within the coupled Hartree–Fock framework to calculate the 1s2s ³S state of helium and heliumlike ions. The results are in very good agreement with those obtained by the use of multiterm correlated wave functions. Some interesting observations associated with the wave function are presented.     

Experimental and theoretical differential cross sections for the N(2D) + H2 reaction

In this paper, we report a combined experimental and theoretical study on the dynamics of the N(2D) + H2 insertion reaction at a collision energy of 15.9 kJ mol(-1). Product angular and velocity distributions have been obtained in crossed beam experiments and simulated by using the results of quantum mechanical (QM) scattering calculations on the accurate ab initio potential energy surface (PES) of Pederson et al. (J. Chem. Phys. 1999, 110, 9091). Since the QM calculations indicate that there is a significant coupling between the product angular and translational energy distributions, such a coupling has been explicitly included in the simulation of the experimental results. The very good agreement between experiment and QM calculations sustains the accuracy of the NH2 ab initio ground state PES. We also take the opportunity to compare the accurate QM differential cross sections with those obtained by two approximate methods, namely, the widely used quasiclassical trajectory calculations and a rigorous statistical method based on the coupled-channel theory.     

Total and angular differential cross sections of electrons emitted in collision between antiprotons and helium atoms

We present total and angular differential single-ionization cross sections for antiproton–helium collisions in the energy range of 1–1000 keV within the framework of time-dependent coupled-channel-, a continuum distorted wave eikonal initial state and classical trajectory Monte Carlo methods. The results are compared with other theoretical results and experimental data.     

The lifetime of the (μHe) 2S + metastable state in helium gas

The ion-clustering mechanism of the quenching of the metastable 2S-state of the muonic helium ion (μHe) _2S ⁺ in gaseous helium is studied on the basis of quantum-chemical calculations of clusters He _n (μHe)⁺. It is shown that the quenching rates do not depend on the cluster ordern atn ≥ 2. In the helium gas at the pressure 0.1 ?p(atm) ? 10 the quenching of (μHe) _2S ⁺ proceeds, mainly, at the vibrationally excited levels of He(μHe) _2S ⁺ cluster, while atp ? 10 atm, at the ground vibrational state of the cluster He₂(μHe) _2S ⁺ . Atp ≥0.1 atm the calculated quenching rates agree with the recent experimental data.     

Parametrization of multiply differential cross sections

Multiply differential cross sections for two- and three-electron escape are parametrised in terms of generalised tensorial asymmetry parameters. The analysis is based exclusivly on rotational invariance as an exact symmetry for the experimental set up. No approximate assumptions are made on the correlated dynamics of many- electron systems. Results are valid for any atomic and molecular target. The new parameters may be used to describe experimental and theoretical data in a compact way, but also to link e.g. coincidence and non-coincidence measurements with each other.     

Measurements of differential cross sections in the backscattering region

A review of experimental techniques which enable detection of electrons scattered in the backward direction, with an emphasis on recent developments in the magnetic angle-changing technique is presented. Results of measurements of differential cross sections for elastic electron scattering in the range of large scattering angles in rare gases and small molecules are discussed and compared with selected theoretical investigations.     

23S state of helium

A rapidly convergent method, which has previously been applied to the ground state of the helium atom, has been extended to excited S states. This method is based on an expansion of the wave function in powers of \documentclass{article}\pagestyle{empty}\begin{document}$ \sqrt {r_1^2 + r_2^2} $\end{document}, ln (r + r), \documentclass{article}\pagestyle{empty}\begin{document}$ w = r_{12} /\sqrt {r_1^2 + r_2^2} $\end{document}. Different effective nuclear charges are used for the inner and the outer electrons. Very satisfactory results are obtained for expectation values of various operators.     

Parity-dependent rotational rainbows in D2-NO and He-NO differential collision cross sections

The (j', Omega', epsilon') dependent differential collision cross sections of D2 with fully state selected (j = 12, Omega = 12, epsilon = -1) NO have been determined at a collision energy of about 550 cm(-1). The collisionally excited NO molecules are detected by (1+1') resonance enhanced multiphoton ionization combined using velocity-mapped ion-imaging. The results are compared to He-NO scattering results and tend to be more forward scattered for the same final rotational state. Both for collisions of the atomic He and the molecular D2 with NO, scattering into pairs of rotational states with the same value of n = j' - epsilon epsilon'2 yields the same angular dependence of the cross section. This "parity propensity rule" remains present both for spin-orbit conserving and spin-orbit changing transitions. The maxima in the differential cross sections-that reflect rotational rainbows-have been extracted from the D2-NO and the He-NO differential cross sections. These maxima are found to be distinct for odd and even parity pair number n. Rainbow positions of parity changing transitions (n is odd) occur at larger scattering angles than those of parity conserving transitions (n is even). Parity conserving transitions exhibit-from a classical point of view-a larger effective eccentricity of the shell. No rainbow doubling due to collisions onto either the N-end or the O-end was observed. From a classical point of view the presence of a double rainbow is expected. Rotational excitation of the D2 molecules has not been observed.     

Effect of orbiting resonance on the elastic differential cross sections

The effects of orbiting resonances on elastic differential cross sections are investigated for the Lennard-Jones (12, 6) model potential. The elastic differential cross section consists of three terms: a resonance term, a potential scattering term and an interference term. The interference term has a significant effect only at small angles of the differential cross section. The importance of the potential scattering term depends proportionally upon the orbiting resonance energy. For the low-lying orbiting resonance states, the resonance term is the dominant term, but at higher energy it appears only in the backward differential cross sections. Generally, by fitting the large angle differential cross sections, the resonance orbital angular momentum can be estimated.     

Measurements of total cross sections for electron scattering from helium and argon

A time-of-flight (TOF) electron spectrometer has been used to measure absolute total cross sections (TCS) scattered from helium and argon over the energy range from 1 to 50 eV. The TOF spectrometer and experimental procedure are described briefly, and experimental results are presented together with associated errors. The results are found to be in good agreement with other experimental and theoretical data.     

Collision cross sections for excitation energy transfer in Na* (3P 1/2)+K(4S 1/2)⇔Na*(3P 3/2)+K(4S 1/2) processes

The cross sections for the excitation energy transfer between the 3² P _J states of sodium atoms by collisions with ground-state potassium atoms have been measured by resonant Doppler-free two-photon spectroscopy, where the population densities of directly pumped and collisionally excited Na(3P _J )(J=1/2, 3/2) levels were probed by counter-propagating Na(3P _J ) → Na(4D _{3/2, 5/2}) excitation and detected with the thermionic diode. Cross sections of σ(3P _1/2 → 3P _3/2)=190 Ų±20% and σ(3P _3/2 → 3P _1/2)=100 Ų±20% were found. The theoretical calculations taking into account the long-range interaction termsR ^?6,R ^?8 andR ^?10 yield a value σ(3P _1/2 → 3P _3/2)=165 Ų. On the basis of these long-range interaction potentials the differential cross section has been calculated and compared with recently published experimental data. Very good agreement between the theoretical and experimental data was found.     

Measurement of angular dependencies of M X-ray differential cross sections and production cross sections using 5.96 keV photons

The differential cross sections of the emission of M-shell fluorescence X-rays from Tl and Pb have been measured by 5.96 keV photons at seven angles ranging from 50° to 110°. The differential cross section is found to decrease with the increasing emission angle, showing an anisotropic spatial distribution of M-shell fluorescence X-rays. Furthermore, M-shell fluorescence cross sections and the average fluorescence yields were measured for Pt, Au, Hg, Tl, Pb, Bi, Th, and U at an excitation energy of 5.96 keV using a Si(Li) detector. The experimental results of the total M X-ray fluorescence cross sections and M-shell fluorescence yields were compared with the theoretical values.This revised version was published online in November 2005 with corrections to the Cover Date.     

Rotational rainbows in inelastic atom—molecule differential cross sections

The existence of rotational raibows in atom-rigid rotor inelastic differential cross sections is shown by considering the classical limit of the centrifugal sudden-rotational sudden expression for the scattering amplitude.     

The total ionisation cross section and the large angle differential cross section for the system He(21S, 23S) + Ar,N2

We have measured the total ionisation cross section Q_ion(g) and the large angle differential cross section σ(θ, g) for the system He(2¹S, 2³S)+ Ar, N₂ at energies 0.05 < E_c.m. (eV) < 6. This energy range is covered by applying two different discharge sources for the production of metastable atoms. In the atomic beam the He(2³S) level is most abundant with relative populations C = 0.91±0.01 and C = 0.96±0.01 for thermal energy range and the superthermal energy range, respectively. A quench lamp is used for the quenching of the (2¹S) level population. In the thermal energy range, σ(θ, g) and Q_ion(g) are in fair agreement with experimental results of other authors and with calculated cross sections based on the optical potential given by Siska. In the superthermal energy range, the He(2³S)+Ar optical potential is modified to describe our experimental data. The slope of the repulsive branch of the real potential is increased for r < 2.85 Å; in the imaginary potential a saturation to a constant (or even decreasing) value for internuclear distances less than 2.5 Å is introduced.     

Total photon attenuation cross sections of helium at energies below 10 keV. An assessment of the accuracy of measured and calculated cross sections

Recent measurements and calculations of helium photoionization, photon attenuation and scattering cross sections for energies below 10 keV are critically evaluated and compared with older measurements, calculations and tabulations. Oscillator strength sum rules are used to assess the validity of various results.     

Total cross sections of electron collisions with S atoms; H2S,OCS and SO2 molecules (Ei ≥ 50 eV)

Collisions of intermediate to high energy electrons are considered with S-atoms as well as H₂S, OCS and SO₂ molecules as targets. We employ e^- atom total cross sections calculated in the complex optical potential, to calculate e^--molecule total cross sections in a simple and a modified Additivity Rule. Our total (elastic + inelastic) cross sections above 50 eV, fare reasonably well as compared to various experimental and theoretical data. The calculated inelastic cross sections serve as the upper limit of total ionization cross sections. Results are presented graphically from about 10 to 5000 eV.