bluuebunny/crossref_metadata_2025 huggingface dataset:
Stark broadening of Si III and Si IV lines
Authors: M Platisa  , M Dimitrijevic  , M Popovic  , N Konjevic
Published: July 2002

The halfwidths of seven Si III and four Si IV lines have been measured in a pulsed arc. The electron density of 5.8*1016cm-3was determined by laser interferometry, while the electron temperature of 25600 K was measured from a Boltzmann plot of the relative intensities of the Cl III lines. The experimental Si III and Si IV Stark-profile halfwidths were compared with calculated values obtained from Baranger's semiclassical (1962) and Griem's semiempirical (1968) approaches. The agreement between experiment and semiempirical (1968) approaches. The agreement between experiment and semiempirical results is within 15%.
Laser-induced ionising collisions in alkali vapours
Authors: S Geltman
Published: July 2002

The semiclassical theory is developed for a simultaneous collisional and radiative process,, and applied to the laser-induced ionisation in a collision of two excited alkali atoms (in their lowest n2P states) in a laser field. Perturbation theory is used to evaluate the probability for this process in the case of straight-line paths at large impact parameter. The collision perturbation is taken to be the dipole-dipole interaction between the two atoms, which together with the dipole interaction with the radiation leads to the occurrence of s and d intermediate atomic states and p and f final states for the ejected electron.
Si KαX-ray emission spectra of Si, SiC, SiO2and Si3N4
Authors: G Graeffe  , J Juslen  , M Karras
Published: July 2002

Si Kalphaspectra from Si, SiC, SiO2and Si3N4have been measured in fluorescence by using a double crystal spectrometer. The chemical shifts, the linewidths as well as relative intensities have been observed for Kalpha 12as well as for Kalphasatellite lines. The measured Kalpha 1X-ray width is 0.43 eV. The chemical environment affects all Kalphalines and this effect is especially strong on the satellite lines. Satellite structure in pure silicon is discussed based on the TOP calculations of Aberg et al. as well as on intermediate coupling.
High-energy behaviour of the transition probabilities and total cross sections for charge exchange
Authors: Dz Belkic
Published: July 2002

A second-order method for charge exchange is introduced. Using the impact-parameter method, a transition amplitude for the ground-state capture from atomic hydrogen by fast protons is obtained in closed analytical form. At vanishingly small impact parameters rho , the Brinkman-Kramers (BK) transition probability (behaving as nu-10with increasing incident velocity nu ) is found, but reduced by the factor 0.2857. At large impact parameters, the dominant contribution arises from the second-order effects in the second-order in the electron-proton interaction. Total cross sections for the capture into 2s and 3s states of atomic hydrogen in H++H(1s) collisions as well as for the capture summed over all final discrete states of H are in excellent agreement with experimental data.
Laser spectroscopy of collisional coherence transfer
Authors: S Stenholm
Published: July 2002

Considers the transfer of optical coherence from one level pair to another. The effect is isolated from the general collision expression derived by Berman (1976) and it is argued that it is best observed in transient measurements. The free decay of a four-level system is solved analytically and two regimes are found: one with oscillations displaying a beat and another with two decay rates. At the border the exponential dependence is modified. The implications for free induction decay and echo experiments are presented. Both phenomena can be used to detect the collisional transfer of coherence, and some experimental aspects of their observation are discussed.
Direct laser-based measurements of the collisional depopulation rate of the n=2 level of hydrogen in a plasma
Authors: D D Burgess  , G Kolbe  , J M Ward
Published: July 2002

A laser-based method of preparing a plasma with only a single atomic-state population significantly out of equilibrium is described. This technique allows determination of collision rates for first excited states largely free from the problems of multiple-level excitation and cascade inherent in most fluorescent scattering techniques in plasmas, or from the absolute intensity measurements in the VUV inherent in emission spectroscopic techniques. The results obtained for the n=2 state of hydrogen, however, pose severe problems in interpretation in terms of presently accepted electron collision rates.
On the role of dipole transitions in the semiclassical approximation for K-shell ionisation
Authors: P A Amundsen
Published: July 2002

The role of the dipole-transition amplitude in the inner-shell ionisation of atoms by light ions is discussed within the framework of the semiclassical approximation. Analytical expressions for the projectile path factors for a hyperbolic projectile path are reported. The recoil of the target nucleus during the collision is taken into account by an extra non-inertial term in the electronic Hamiltonian, both for a relativistic and a non-relativistic electron description. The recoil correction strongly modifies the dipole amplitude at small impact parameters. The effects of binding and symmetrisation are also briefly discussed. Numerical results are reported for calculations of K-shell ionisation.
Measurement of the ion-mass effect on the central structure of Hβin a plasma produced by a combustion-driven shock tube
Authors: J L Chotin  , J L Lemaire  , J P Marque  , F Rostas
Published: July 2002

The central structure of the Stark-broadened Balmer line Hbetahas been analysed in the plasma produced behind the reflected shock in a combustion-driven shock tube of internal diameter 10 cm. The incident shock is propagated at a Mach number typically of M=8 in a mixture of 0.5% H2(D2), 80% Ne, 20% He (Ar) at an initial pressure of 10 Torr creating in the reflected-shock region temperatures close to 104K and electron number densities 1016<Ne<1017. Measuring times are 150 mu s. The variation of centre dip with reduced mass which has now been measured in two widely differing plasma sources strongly suggests that the discrepancy between theory and experiment for the central structure of Hbetais due to ion dynamical effects.
Ejected-electron spectroscopy of autoionising states of CO using an electron-electron coincidence technique
Authors: D G Wilden  , P J Hicks  , J Comer  , A Weingartshofer
Published: July 2002

Quantitative measurements have been made of the relative intensities for electron-emitting transitions from autoionising levels of carbon monoxide to vibrational levels of the ground electronic state of CO+, following electron impact excitation. An electron-electron coincidence technique was used, in which the scattered electrons which had excited a selected autoionising level, and ejected electrons resulting from subsequent autoionisation processes were detected in separate analysers. The measured intensities are compared with Franck-Condon calculations using Morse potentials to represent the autoionising levels and ion levels. The results obtained indicate that the equilibrium internuclear separation for the autoionising levels is 1.243+or-0.001 AA, very close to that for the A2Pi state of CO+, which is the probable series limit. Previous assignments of the autoionising levels, based on photoabsorption and photoelectron spectra, are discussed in the light of the present results.
Determination of relative oscillator strengths of the copper resonance lines by atomic absorption spectroscopy
Authors: P Hannaford  , D C McDonald
Published: July 2002

The relative oscillator strengths of eleven resonance lines of copper, having excited levels belonging to the configurations 3d94s4p, 3d104p and 3d105p, have been determined from atomic absorption measurements of the radiation emitted from a copper hollow-cathode lamp. Allowance is made in the analysis for the effect of differences in the hyperfine structures of the lines. The results are interpreted by considering the effects of configuration interaction and departures from LS coupling, using mixing coefficients derived by Landman et al. (1969).
One- and two-photon ionisation of the 3s and 3p states of Na I
Authors: C Laughlin
Published: July 2002

A model-potential method is used to compute one- and two-photon ionisation cross sections for ground- and excited-state sodium atoms. The inhomogeneous-differential-equation method, suitably modified for use in resonance regions, is used in the two-photon calculations. The author calculates a generalised cross section of the order of 10-48cm4s for two-photon ionisation of the 3p level at the Na I resonance transition wavelength.
Modified binary encounter model for proton impact K-shell ionisation of atoms
Authors: A Kumar  , B N Roy
Published: July 2002

The Coulomb deflection of a projectile due to the target nucleus and the increase in the binding of a target electron due to incident protons have been incorporated in a binary encounter model for proton impact K-shell ionisation of atoms. The modified expressions have been used to calculate K-shell ionisation cross sections for different atomic systems. The cross sections have also been calculated by using Vriens' expression (1966, 1967) with a Hartree-Fock velocity distribution for the bound electron. These results have been compared with other theoretical calculations for the bound electron. These results have been compared with other theoretical calculations and the available experimental data. The modified model gives good results for the ionisation cross sections for low-energy protons and results based on Vriens' expression using the Hartree-Fock velocity distribution agree well with the experimental results at high incident energies.
Electron scattering resonances using dilatation transformations. II. Restricted perturbation methods
Authors: P Winkler
Published: July 2002

For pt.I see ibid., vol.11, no.8, p.1475 (1978). In the present text two different perturbation methods are proposed, the implementation of which facilitates the computation of resonance parameters within the framework of the coordinate-rotation method. Additional physical insight into the application of dilatation transformations in connection with finite-basis techniques is gained. The virial theorem for resonances derived in the companion paper supplies a rigorous criterion for determining the best solution (in a variational sense) obtainable at a given level of the approximation. This is a generalisation of the well known scaling relationships for wavefunctions, investigated by Lowdin, to include the case of resonance states. The test system is the first1S resonance of the He++e system for which there is ample numerical data from previous standard coordinate-rotation calculations.
The XUV spectra of highly ionised molybdenum
Authors: M W D Mansfield  , N J Peacock  , C C Smith  , M G Hobby  , R D Cowan
Published: July 2002

The spectra of molybdenum ions produced in Tokamaks in the wavelength range 10-200 AA have been reproduced in a plasma formed by laser beam irradiation of solid molybdenum targets. Lines from highly ionised stages of molybdenum (Mo XXX to Mo XXXII) have been distinguished by varying the laser beam intensity. Detailed analyses of the simpler ions, Mo XV (Ni-like), Mo XVI (Co-like), Mo XXXII (Na-like), and to a lesser extent Mo XXXI (Mg-like) and Mo XVII (Fe-like), have been achieved by comparison with ab initio calculations. A general interpretation of intermediate ion stages is also given but it is shown that most of these spectra are so complex, as a result of inner-subshell excitation, that detailed term-scheme analyses are nearly impossible.
Many-electron effects in the 3p X-ray photoelectron spectrum of Kr
Authors: M Ohno  , G Wendin
Published: July 2002

The X-ray photoelectron spectrum of Kr in the neighbourhood of the main 3p lines has been calculated using diagrammatic many-body theory for the 3p self-energy and spectral function. Super Coster-Kronig 3p to or from 3d2epsilon f dipole fluctuations are found to shift the 3p lines by about 3 eV from their Delta SCF positions, the dipole shift being approximately 30% of the Delta SCF monopole relaxation shift. For determining the 3p linewidth the 3p to 3d4s epsilon p and 3p to 3d4p epsilon d Coster-Kronig transitions and the super Coster-Kronig transitions are approximately equally important. The calculated positions and widths of the 3p main lines are in good agreement with experiment.
Velocity dependence of fine-structure changing collisions of Na with Ne, Ar, Kr, Xe, N2and CO2
Authors: J Apt  , D E Pritchard
Published: July 2002

The authors present measurements of the velocity dependence and absolute magnitude of the fine-structure changing collision cross section for Na(3p) in collisions with Ne, Ar, Kr, Xe, N2and CO2. The measurements were made in a gas cell using a technique based on the Doppler shift to achieve the velocity selection. The validity of the technique is established both by careful study of possible systematic effects and by comparison with recent crossed beams measurements where available. The results for rare-gas targets are compared with both semiclassical and quantal calculations; those by Pascale and Olson given excellent agreement for Ar, good for Xe (the calculated magnitude is too big), and fair for Ne and Kr (both magnitude and velocity dependence are somewhat outside error). The N2results agree with the magnitude of recent calculations. The CO2results are anomalously small at low relative velocity; this is attributed to competition from quenching processes.
Ion-ion capture collisions in the continuum distorted-wave approximation
Authors: S Mukherjee  , N C Sil
Published: July 2002

The continuum distorted-wave approximation of Cheshire (1964) is applied to the case in which a nucleus of charge Z' captures an electron attached to another nucleus of charge Z. Numerical results for the total capture cross sections have been obtained for the particular cases of electron capture from the targets He+, Li2+, Be3+and C5+by protons into the ground state or the excited 2s state. Capture by alpha particles from He+, Li2+and Be3+into the ground state or the excited 2s state are also considered. Wherever possible comparisons are made with the Coulomb-Born results.
Atomic X-ray scattering factors for forward scattering beyond the dipole approximation
Authors: M S Jensen
Published: July 2002

It is shown that the usual dispersion formula used in all calculations of the real part of the anomalous scattering factors, f', is only valid within the dipole approximation. A new correction term which is positive and of the order of Etot/mc2, with Etot the total binding energy of the electrons in the atom, is needed. Based on experimental data, the K-shell contribution to the new correction for f' is found to be larger than 0.013 for Si and 0.073 for Ge. Formulae expressing a total K-shell photoelectric cross sections in terms of the dipole approximation values are given. It is concluded that at present no theoretical calculations give f' better than to within an accuracy of the order -Etot/mc2.
Multichannel variational calculations of low-energy electron-molecule collisions: static exchange approximation
Authors: L A Collins  , W D Robb
Published: July 2002

Kohn and inverse Kohn variational procedures are used to study the scattering of electrons by closed-shell diatomic molecules in the static exchange approximation. The trial wavefunctions are constructed from free particle, continuum static and bound orbitals. Variational corrections are obtained to the wavefunction as well as the reactance matrix. Various forms of the trial wavefunction are applied to collisions of electrons with H2, N2, LiH and CO, and the resulting eigenphases compares with exact static exchange results. For non-resonant symmetries, the method produces results within 10% of the exact results. Resonance widths and positions are predicted within 25% or better.
Systematic theoretical study of the Stark spectrum of atomic hydrogen. II. Density of oscillator strengths. Comparison with experimental absorption spectra in solid-state and atomic physics
Authors: E Luc-Koenig  , A Bachelier
Published: July 2002

For pt.I see ibid., vol.13, no.9, p.1743 (1980). Absolute values for the density of oscillator strengths in the photoabsorbtion spectrum of hydrogen-like atoms in the presence of a uniform electric field are calculated using the wavefunctions obtained from the method described in the previous paper. The symmetry properties of the wavefunctions with respect to the plane z=0 are analysed-z is the direction of the electric field. Cancellation effects can appear in the calculation of oscillator strengths due to the symmetry properties of the wavefunctions and of the polarisation of the light. The hydrogenic model is used to interpret the structures observed in the absorption spectra of alkali atoms and of semiconductors in the presence of an external electric field.
Positron drift in molecular hydrogen
Authors: N Bose  , D A L Paul  , J -S Tsai
Published: July 2002

Measurements of positron drift in H2gas have been made in the pressure range 10-200 Torr between 0 and 4 Td. A shape analysis gives a universal function W/Zeff. Using the annihilation parameter Zeff=13.6, the drift speed W increases linearly up to 2.9*105cm s-1at 1 Td. Above 1.4 Td there is evidence for positronium formation. These are the first measurement of positron drift speeds.
Two- and three-body electron attachment in air
Authors: B I Schneider  , C A Brau
Published: July 2002

The rate of disappearance of electrons has been measured in mixtures of 20% O2in N2. The results show a three-body attachment rate coefficient of 2*10-32cm6s-1for electron mean energies in the range from 0.6 to 1.8 eV. The results also show a two-body rate coefficient which decreases from 8*10-13to 5*10-14cm3s-1over this same range.
Observations of gains in the extreme ultraviolet
Authors: D Jacoby  , G J Pert  , L D Shorrock  , G J Tallents
Published: July 2002

Observations of gain on the hydrogen-like carbon ion Balmer- alpha transition, C VI Halpha, at 182 AA are examined for consistency and possible sources of error. It is concluded on purely experimental grounds that the only result consistent with the full set of data is that amplification is observed, and that this should be ascribed to gain by stimulated emission. The data are compared with the values obtained by computational modelling and shown to be in satisfactory agreement provided the incomplete burn through is taken into account in accord with the numerical predictions. It is found that the model severely underestimates the gain observed: reasons for this are given.
Bohr orbit theory revisited. I. Ground-state energies for the helium isoelectronic sequence
Authors: R D Harcourt
Published: July 2002

The (non-relativistic) ground-state energies for H-, He, Li+, C4+and Ne8+are calculated using the 1913 orbit model of Bohr for a two-electron atomic system, modified so that the electrons are able to move away from Bohr's 180 degrees arrangement of them around the orbit. Both classical and non-classical weighting factors (P( phi )) are associated with the energy E( phi ) for angle phi . If phi is restricted so that E( phi ) cannot exceed the energy of He+, then the calculated average energies E for He(-2.900 or -2.908 au, with classical and non-classical P( phi )) are much closer to the exact energy (-2.9037 au) than is Bohr's estimate (-3.0625 au). Similar calculations for H-and the isoelectronic cations give values for E that are respectively rather less than and greater than the exact energies. For H-, with a classical P( phi ), a simple further modification gives E=-0.52793 au; the exact energy is -0.52775 au. For He, Ne8+and Ca18+the results of approximate calculations are also reported, which allow for the possibility that the two electrons move around separate orbits when phi is small. Relationships are developed between the orbit and orbital models for the ground states of two-electron systems.
Charge exchange in the O8+-He collision at keV amu-1energies
Authors: S Bliman  , D Hitz  , B Jacquot  , C Harel  , A Salin
Published: July 2002

Charge exchange between O8+and He(1s2) is studied both theoretically and experimentally. In the energy range where capture cross sections have been measured good agreement is obtained between theory and experiments. Calculations predict that in single-electron capture the electron is transferred dominantly into O7+(n=4), which is supported by earlier experimental work.
Interatomic potentials for the Hg-Xe system from measurements of the temperature-dependent absorption spectrum
Authors: T Grycuk  , M Findeisen
Published: July 2002

The absorption profile and the temperature dependence of the Hg resonance line at 253.7 nm perturbed by Xe at a density of about 1*1019 atoms/cm3 have been carefully studied with a high-resolution double beam spectrometer. Interatomic potentials for Hg-Xe in the ground electronic state 1O+ as well as the excited state 3O+ in a wide range of separations (from a repulsive wall up to the van der Waals attraction region) have been deduced from the spectrum. Some important results for the excited 31 state, in particular the van der Waals coefficient C6, are also obtained. The ground-state potential with well parameters of epsilon =240+or-10 cm-1 and Rm=4.10+or-0.03 AA, derived experimentally without recourse to any external data, is well reproduced by the Maitland-Smith (1973) ( epsilon , Rm, alpha , beta ) function for alpha =11 and beta =17. The well depth for the 3O+ excimer state is found to be 1450+or-100 cm-1 at a separation of 3 AA. The 1O+ to 3O+ transition moment in the range of separations considered seems to be independent of R.
Ionisation and appearance potentials of CH4by electron impact
Authors: P Plessis  , P Marmet  , R Dutil
Published: July 2002

The CH4+electroionisation efficiency curve and the CH3+, CH2+, CH+and C+appearance potential curves are presented. The data were obtained by an apparatus of very high sensitivity with an improved electron monochromator. The CH4+ionisation potential is measured to be 12.63+or-0.02 eV. The results show that some previously reported appearance potential values should be corrected, in some cases by several electron volts. This is attributed to superior apparatus sensitivity. Ion-pair formation is clearly observed for the CH3+and CH+fragments. The CH+and C+appearance potentials have been detected down to adiabatic threshold. The stable fragment CH22+, is also observed.
Rotationally resolved electron-photon coincidence study of H2(d3Πu) exciton
Authors: J W McConkey  , S Trajmar  , J C Nickel  , R McAdams
Published: July 2002

The three normalised Stokes' parameters characterising the decay of the electron impact excited d3piu( nu1=0, N1=1) rotational level of H2were determined in an electron-photon coincidence experiment at 25 eV impact energy and 60 degrees scattering angle. The low degree of polarisation (coherence) which was observed could be caused by both the averaging over the magnetic sublevels of the ground state of the target and the fine and hyperfine relaxation process. The average angular momentum transfer perpendicular to the scattering plane from the electrons to the molecules was found to be near zero in this excitation process.
Green's function approach to the electron shift and broadening of spectral lines in non-ideal plasmas
Authors: L Hitzchke  , G Ropke  , T Seifert  , R Zimmermann
Published: July 2002

Expressions for the electron shift and broadening of spectral lines in dense plasmas are derived on the basis of a recently given Green's function approach to the dielectric function. It is shown that in the case of not too high densities these expressions are equivalent to those following from the semiclassical impact approximation. Estimates are given for the shift and broadening of some argon lines.
Hβprofiles at high electron densities from optical discharges
Authors: C Carlhoff  , E Krametz  , J H Schafer  , J Uhlenbusch
Published: July 2002

In continuous optical discharges, plasmas with temperatures of about 104K and with electron densities of the order of 1024m-3can be produced. The discharge is generated by a 5 kW CW CO2laser focused into a chamber filled with hydrogen at a pressure of several MPa. The calibrated line intensity of Hbetawas monitored by means of an OMA system with spatial and frequency resolution. The measurements yield Stark-broadened Hbetaprofiles from which, using Saha's equation, the electron temperature and density can be derived. The asymmetry of the Hbetaline increases from 8% at ne=4*1023m-3to 14% at ne=1.2*1024m-3, in rough agreement with theoretical predictions, whilst the half width of the line is in good agreement with theory in the same electron density interval.
Experimental study of Hαbroadening and shift in dense argon plasmas
Authors: Y Vitel
Published: July 2002

The line profile of Halphais measured in plasmas produced in liner flashtubes. The electron densities are in the range 6*1017-1018cm-3measured by independent methods. The full widths at half maximum of Halphaare given. At Ne=1018cm-3, the experimental and the theoretical profiles are compared. The red shift is measured and varies linearly with the electron density, in agreement with some theoretical work.
An experimental investigation of the ejected-electron spectra arising from autoionising and Auger transitions in Eu I and Eu II excited by electron impact for the range of incident-electron energies from 20 to 500 eV
Authors: M J Ford  , L F Forrest  , V Pejcev  , D Smith  , R S Sokhi  , K J Ross
Published: July 2002

The ejected-electron spectra of europium arising from autoionising and Auger transitions in Eu I and Eu II following excitation by electron impact have been measured in the energy region from 0 to 27 eV; incident-electron energies were in the range from 20 to 500 eV. 151 spectral features are tabulated and excitation functions are reported for a number of autoionising and Auger transitions. The chemi-ionisation electron spectrum of europium atoms reacting with oxygen and water vapour is reported in the electron energy region from 0 to 1.5 eV.
Spin-polarised SCC-Xα calculations for electronic- and magnetic-structure properties of (2Fe-2S) ferredoxin models
Authors: R Blas  , J Guillin  , E L Bominaar  , M Grodzicki  , V R Marathe  , A X Trautwein
Published: July 2002

The spin-polarised SCC-X alpha method is used for the evaluation of electronic- and magnetic-structure properties (i.e., electron densities at the iron nuclei, electric-field gradients, g factors and magnetic hyperfine tensors) of oxidised and reduced (2Fe-2S) ferredoxin models, represented by the structure formula ((SR)2FeS2Fe(SR)2) (n=-2, -3), with R=H, CH3and (C6H4(CH2)2)12/. A strong geometry dependence of charge and spin densities, and their related properties, is found for minimal cluster size (R=H) on the position of the terminal hydrogen atoms. A Fe-S-H bond angle of about 90' turned out to be preferable to 180'. Experimental hyperfine data of synthetic analogues and of ferredoxins are in reasonable agreement with corresponding calculated properties obtained for the (2Fe-2S) ferredoxin models mentioned above. Comparing experimental and calculated g factors of reduced (2Fe-2S) centres indicates that the model clusters used are of gavapproximately 1.91 type. Finally, the exchange-coupling constant J between the two iron ions in the oxidised (2Fe-2S) ferredoxin model is estimated from the difference in the total energy between the high-spin and broken-spin symmetry states of the model.
Applications of pulsed microwave-microwave double resonance: I. Relaxation studies in gases
Authors: D A Andrews  , J G Baker
Published: July 2002

The time-resolved response of a gas absorber exposed to two independent sources of microwave radiation, one steady and the other pulsed, is described using a formalism based on the Bloch equations for a three-level system. This predicts that a series of experiments can be made on the resonant and off-resonant recoveries of the absorptive and dispersive properties of a single sample by which the individual collisional relaxation parameters that characterise its rotational states may be separately measured. Some of these can be determined only by double-resonance experiments. The construction and operation of amicrowave double-resonance bridge spectrometer capable of carrying out these experiments is described, and results obtained for the (J=2 from 1)-(J=1 from 0) system of OCS are discussed in detail. The polarisation relaxation rate for the 2 from 1 transition is found to be 38.2(2) mu s-1Torr-1and its population relaxation rate, including cross-relaxation effects, is found to be 38.9(1.9) mu s-1Torr-2. Values for the cross-relaxation parameters are obtained for the first time.
Adiabatic representation for the three-body problem in hyperspherical coordinates. I. Statement of the problem
Authors: M B Kadomtsev  , S I Vinitskii
Published: July 2002

For the three-body Coulomb problem a hyperspherical parametrisation of independent variables is given on a five-dimensional sphere S5with a hyperradius RH, the first linear invariant of the inertia tensor. The hyperspherical adiabatic basis is defined as a complete set of eigenfunctions and eigenvalues of the Hamiltonian on the sphere S5for every fixed value of the slow variable RH. The partial wave analysis in the total momentum J representation allows the authors to separate three Euler angles and to reduce the hyperspherical problem on S5to a system of (J+1) two-dimensional problems. Classification is given of the hyperspherical adiabatic basis for small and large values of the hyperradius RH. The logarithmic Fock singularity at the point of triple collision (RH=0) is explicitly shown. The approach is assigned to computing the cross sections of mesic atomic processes in the muon catalysis problem.
Electron detachment in oxygen
Authors: M J Eccles  , B C O'Neill  , J D Craggs
Published: July 2002

Using a double ionization chamber in one half of which negative ions are formed and in the other half of which they suffer detachment, experiments on the collisional detachment from O3-and O2-in oxygen at E/p at 20 degrees C equal to 45-50 V cm-1torr-1give values for the detachment coefficient per unit pressure delta /p approximately 0.01. Pressure variations (20-60 torr) are discussed. For Townsend discharges in these circumstances in oxygen detachment is thus relatively unimportant, in that delta << eta (the attachment coefficient).
Absolute oscillator strength of the (0.0) band of the gamma system of nitric oxide by the hook method
Authors: A Pery-Thorne  , F P Banfield
Published: July 2002

The hook method has been adapted for molecular spectra to allow a determination of the absolute oscillator strength of a band from measurements on a single hook near the band head. For the A2Sigma+-X2II system of nitric oxide, the value f00=(3.64+or-0.05)*10-4was obtained, in good agreement with previous measurements on the integrated absorption at high pressures. The behaviour of f00as a function of pressure was investigated at pressures up to 7 atm of nitric oxide and 35 atm of argon, but no variation was found. The relation between f00and the latest experimental value for the lifetime of the v'=0 vibrational level is discussed, using recent measurements for the variation of electronic transition moment with r centroid; the inconsistencies between these three sets of measurement prove to be considerably larger than the apparent experimental errors.
Collisional quenching of metastable deuterium
Authors: V Dose  , W Hett
Published: July 2002

The cross section for collisional quenching of metastable deuterium in collisions with molecular hydrogen has been measured for velocities between 0.35*106 and 8*106 cm s-1 using a time of flight method. Results are compared with theoretical predictions and other experimental work in this velocity range.
A redetermination of the thermal diffusion factor for some inert gas mixtures. I
Authors: K E Grew  , W A Wakeham
Published: July 2002

As a result of improvements in the method of analysis of gas mixtures, which permit detection of changes in mole fraction of 1 part in 105, a redetermination of the thermal diffusion factor for some gas mixtures of special interest in progress. Results are given here for argon-neon and krypton-argon mixtures. The intermolecular potential functions commonly used in connection with other transport properties of gases fail to account for the observed variation of the thermal diffusion factor at temperatures approaching the condensation point of one of the components, and this is attributed to dimerization.
Equilibrium charge distributions of C, N, O, and Ne in carbon foil
Authors: R Girardeau  , E J Knystautas  , G Beauchemin  , B Neveu  , R Drouin
Published: July 2002

Equilibrium charge distributions of C+, O+, N+, and Ne+beams in carbon foil have been measured for incident energies of 1 to 5 MeV. There is consistent agreement with previous work in those regions where there are data in common. Charge state equilibrium is reached in foils at least as thin as 6 mu g cm-2.
Autoionization spectrum of cadmium vapour by electron impact
Authors: J B P Wickes  , K J Ross  , W R Newell
Published: July 2002

Autoionizing transitions in cadmium vapour have been studied by direct observation of the energy distribution of autoionized electrons when the system is excited by electron impact. Two new states have been observed and it is thought that they correspond to transitions autoionizing into the continuum of CdII having energies of 29.34 and 30.00 eV.
Einstein A coefficients, band oscillator strengths and absolute band strengths for the comet-tail band system of CO+
Authors: D C Jain
Published: July 2002

The variation of the transition moment, Re(r), with the internuclear separation for the comet-tail band system of CO+has been studied by the method developed by Jain and Sahni (1968). The expression for Re(r) has been used to calculate the Einstein A coefficients, the band oscillator strengths and the absolute band strengths for this system.
Collisional detachment of electrons and ion molecule reactions in oxygen
Authors: B C O'Neill  , J D Craggs
Published: July 2002

Collisional detachment in oxygen was studied for pressures of about 20-60 Torr and with mass analysis which also allowed conversion rates to be calculated. For O-, delta1/N (detachment coefficient/gas density) was found to be about 5*10-18cm2at E/N (field strength/gas density) of about 50 Td where for O2-, delta2/N approximately 1*10-18cm2. The need for an accurate measurement of the conversion rate for O-to O2-is emphasized.
The formation of N2O+(A2Σ+(0,0,0)) by photoionization of N2O
Authors: H Hertz  , H W Jochims  , W Sroka
Published: July 2002

The dependence of the relative cross section for the process N2O(x1Sigma+(0.0.0)) +h nu to N2O+(A/sup /2Sigma+(0,0,0))+e-on the incident photon energy has been measured between 16.4 and 20.3 eV via the fluorescent radiation of the transition N2O+(A/sup /2Sigma+(0,0,0) to X/sup /2Pii(0,0,0)). It is strongly influenced by Tanaka's apparent emission series R IX and the Rydberg series R VI and R VII.
Influence of ion dynamics on Hα and Hβ at low densities
Authors: J Cooper  , E W Smith  , C R Vidal
Published: July 2002

Calculations for the Stark broadening of H alpha and H beta using a unified theory for both ions and electrons are presented in the density range 1014to 1015cm-3at a temperature of 104K. Although the theory is of marginal validity at these densities, it shows quite conclusively the influence of ion dynamics in reducing the dip at the centre of the H beta profile and the peak in the centre of the H alpha profile.
Spin-orbit coupling photoionization
Authors: T E H Walker  , J T Waber
Published: July 2002

Dirac-Slater calculations are used to predict the ratio of photoionization cross sections for the j=l+or-1/2 components of an atomic orbital. It is shown that the ratio is larger or smaller than the statistical value of l+1:l depending on whether the partial cross section is rising or falling. Two effects are shown to determine the deviation from the statistical ratio, one arising from small differences in the bound state orbitals, and the other from differences in the kinetic energy of the photoelectrons. Differences between the asymmetry parameter, beta , for the two ionizations are found to be small except at the Cooper minimum. In general the primary cause of the two values of beta not being the same at low photoelectron energies is the kinetic energy effect.
Electron-ion coincidence measurements of CH4
Authors: C Backx  , M J Van der Wiel
Published: July 2002

Measurements are reported of 10 keV electron scattering in CH4at low momentum transfers, in coincidence with the various ionic products. Ion mass separation was performed in a time-of-flight system with total transmission for fragments with dissociation energies up to 20 eV. Results have been obtained on the oscillator strengths for the formation of all ionic products for energy losses from the IP up to 80 eV. The present results confirm earlier electron-electron coincidence measurements of the photoionization efficiency (see ibid., vol.8, no.18, p.3007 (1975)) and extend them to higher energy. The oscillator strengths of the (1t2)-1, (2a1)-1and higher initial states of CH4+could be extracted separately from the data.
Configuration interaction studies of bound, low-lying states of N2-, N2, N2+and N22+
Authors: E W Thulstrup  , A Andersen
Published: July 2002

Complete valence shell CI calculations have been carried out for a large number of non-Rydberg states of N2molecule and related ions. Full potential curves are presented for these states, and are used for a calculation of spectroscopic properties. Comparison is made with experimental data where such are available, and several new states and their properties are predicted. Some of these are of great interest in connection with the observation of unidentified states in recent experiments.
Rotational excitation in e--N2scattering
Authors: N Chandra
Published: July 2002

The angular distribution expression for scattering of a structureless particle from a rigid rotating diatomic molecule has been simplified by using the angular momentum recoupling method. The formulae are derived by using this expression to compute the cross sections for transitions among various rotational levels of a diatomic molecule when the e--molecule problem is solved in a body-fixed frame of reference in the fixed-nuclei approximation. The energy dependence of the differential cross section for rotationally elastic and inelastic e--N2scattering has been calculated in the adiabatic-nuclei approximation. The results for the momentum transfer cross section are also given.
Fast-beam, zero-field level-crossing measurements of radiative lifetimes, fine and hyperfine structures in excited states of ionic and neutral beryllium
Authors: O Poulsen  , T Andersen  , N J Skouboe
Published: July 2002

The possible use of level-crossing spectroscopy to study properties of excited states generated by gas excitation of fast ionic beams has been investigated. With a 20-400 keV Be+beam excited by means of helium gas, radiative lifetimes of2D and2F levels in Be II have been determined together with the fine-structure separation of the 5f2F level in Be II and the hyperfine coupling constant for the 2s3d1D level in Be I and the 2p2p level in Be II.
Energy levels for Be I calculated using a model potential and cores approximations
Authors: D W Norcross  , M J Seaton
Published: July 2002

A two-electron model Hamiltonian, used for Be I, includes a core polarization potential Vpol(1,2) which has asymptotic form Vpolapproximately - alpha ((r1/r12)+(r2/r22))2where alpha is the polarizability of Be III 1s1. Solutions are obtained using a frozen-cores method. Two approximations are considered: (a) uses an expansion with core states Be II 2s and 2p; (b) includes in addition a 3d core orbital with a parameter determined variationally. For the series1S,3S,1P0,3P0,1D,3D,1F0and3F0, results are obtained for all bound states ( epsilon <0) with n0. For the series1P,3P,1D0,3D0converging to Be II 2p, results are obtained for n<or=10 and for n= infinity . The calculated ionization energies are more accurate than those obtained in previous theoretical work.
Quantum-mechanical theory of transfer and relaxation of atomic multipole moments
Authors: G Nienhuis
Published: July 2002

The author points out that the Waldmann-Snider equation leads directly to quantum-mechanical expressions for the rate constants for transfer and relaxation of atomic excited state multipole moments, both in the case of resonant interaction and of foreign-gas perturbation. The rate constants are expressed in terms of quantum-mechanical partial cross sections. The effect of the hyperfine interaction is briefly discussed.
On the validity of the model microfield method as applied to Stark broadening of neutral lines
Authors: A Brissaud  , C Goldbach  , J Leorat  , A Mazure  , G Nollez
Published: July 2002

Certain features of the interactions between atoms and fluctuating microfields are discussed, emphasizing those statistical properties of the microfield which play an important role in Stark broadening. A model microfield is constructed incorporating the most relevant features, and it is shown that the model microfield theory constitutes a completely unified treatment and is a powerful tool for testing certain standard approximations.
Thermal expansion and heat capacity of cuprous chloride at low temperatures
Authors: T H K Barron  , J A Birch  , G K White
Published: July 2002

The linear thermal expansion of a polycrystalline sample has been measured in the ranges 1.5<T<34K, 55<T<90K, and at room temperature; and its heat capacity in the range 1.3<T<16K. Expansion is strongly negative at low temperatures, with Gruneisen parameters gamma0th=-2.4+or-0.4 and gammaminth=-2.71; gammainfinityth=0.75+or-0.15. Debye temperatures are Theta0C=179+or-0.6K, ThetaminC=119K, ThetainfinityC=285+or-10K. The elastic and piezoelectric measurements of Hanson et al. (1974) are used to calculate Thetael=182.2+or-2K, gammael=-1.19+or-0.2. When CuCl is compared with other crystals of zincblende structure, gamma0thand ThetainfinityC/ Theta0Ccorrelate well with increasing ionicity, but no such trend is observed for the depth of the minima in gammath(T) and ThetaC(T).
Localized orbital approach to chemisorption. I. H on W(100)
Authors: D W Bullett  , M L Cohen
Published: July 2002

Atomic (s- and d-) orbitals and an atomic approximation to the potential are used in the chemical pseudopotential secular equation to calculate the covalent binding of an adsorbed monolayer on a transition-metal slab. After showing that the method provides a realistic description of the d-bands in bulk W and Pt the changes which accompany adsorption of hydrogen on W(100) in various surface arrangements are examined. Maximum coverage is found to correspond to occupation of all bridge sites on the W(100) surface ( beta1phase). Bridge sites also provide maximum covalent binding at lower coverage but energy differences between alternative sites are small ( approximately 0.2 eV per H-atom) and ionic effects may stabilize adsorption above atoms in the beta2phase.
Short-wavelength collective density excitations in monatomic liquids
Authors: J W E Lewis  , S W Lovesey
Published: July 2002

Computer simulation data for liquids with generalized Lennard-Jones potentials are analysed with the aim of elucidating the key features required of a liquid for it to support a short-wavelength, collective density excitation. The data suggest that, for high densities, both the repulsive and attractive components of the Lennard-Jones potential must be modified substantially for such a mode to exist, and that softening the potential core does not in itself suffice to induce the correlation necessary for a liquid to support a mode. Viscoelastic theory is shown to provide a good description of the dynamical properties and to provide a useful condition for the existence of a collective density excitation.
A bond charge model for the lattice dynamics of iodine
Authors: A Pasternak  , A Anderson  , J W Leech
Published: July 2002

A lattice dynamical model for crystalline iodine has been investigated. The simple bond charge (SBC) model developed by Parr and co-workers (1968, 69, 71 and 73) for free molecules has been adapted for the iodine molecular crystal to take account of intermolecular as well as intra-molecular covalent bonds. Mode instabilities of previous models are absent from the present calculations. Acceptable agreement with experimental dispersion relations has been achieved using model parameters consistent with the basic concepts of the SBC model. The results strongly support the validity of the SBC model for the covalent bonds between halogen atoms.
Proton tunnelling frequencies in ammonium salts from spin-lattice relaxation
Authors: I Svare
Published: July 2002

Proton reorientation tunnelling in many NH4+salts gives a frequency independent minimum in both T1and T1 rhoat the transition to classical relaxation at about 40-70K. The average tunnel frequency is approximately: f1approximately=4*109Ti1( rho )min,(Hz when T1or T1 rhois in s). Tunnel frequencies are derived from T1and T1 rhomeasurements on NH4ClO4, cubic and trigonal (NH4)2SiF6, (NH4)2SnCl6, (NH4)2Ce(NO3)6, (NH4)2Cr2O7and literature data, and compared with tunnel frequencies calculated from barrier heights.
Itinerant antiferromagnetism in the Hubbard model
Authors: K Eapen  , D K Ghosh
Published: July 2002

The two-sublattice Hubbard model has been solved in approximation schemes which are exact in both the zero bandwidth and small interaction energy limits. It is found that the finite temperature antiferromagnetism, which appears in the Hartree-Fock approximation, does not exist in this scheme. An improved solution which includes effects due to finite lifetime also rules out local moments at finite temperatures. The similarity of this solution with the coherent potential approximation for an AB model is discussed. Inclusion of the resonance broadening effect does not appear to alter the physical nature of the solutions.
Proton relaxation and tunnelling in ammonium hexachlorides
Authors: I Svare  , A M Raaen  , G Thorkildsen
Published: July 2002

Proton T1and T1 rhohave been studied in powders of (NH4)2MCl6where M4+=Pd4+, Pt4+, Te4+, Ru4+, Ti4+, Ir4+and Re4+from 40 to 300K. The activation energies Eafor NH4+motion are 0.61, 0.68 and 1.60 kcal mole-1respectively for the Pd, Pt and Te salts, and Eais a linear function of the lattice dimension for the cubic hexachlorides. (NH4)2TiCl6changes structure at about 244K and (NH4)2RuCl6is non-cubic. Approximate NH4+tunnel frequencies have been derived from the non-classical minima in T1and T1 rhoin good agreement with previous results for other ammonium salts.
Stabilisation of the metallic state at low temperatures in HMTTF-TCNQ under pressure
Authors: R H Friend  , D Jerome  , J M Fabre  , L Giral  , K Bechgaard
Published: July 2002

Measurements are reported of the b axis conductivity of HMTTF-TCNQ under hydrostatic pressures up to 33 kbar, and the room temperature, ambient pressure conductivity anisotropies. The two transitions seen in the conductivity at 49K and 43K at ambient pressure fall in temperature when pressure is applied; the lower transition is absent above 3 kbar and the upper transition falls linearly at 1.5K kbar-1. The low-temperature insulating behaviour at ambient pressure is rapidly replaced by weakly metallic behaviour, which at 10 kbar is very similar to that seen in HMTSF-TCNQ at ambient pressure. At higher pressures the resistivity was still falling at 1.2K. It is suggested that HMTTF-TCNQ above 3 kbar and HMTSF-TCNQ at ambient pressure undergo distortions on predominantly one type of stack. A unified picture of the pressure behaviour of this series of TCNQ salts is presented; the Peierls distortions in TTF-TCNQ and TSF-TCNQ occur when the transverse conduction is diffusive and the system is in the one-dimensional regime, whereas HMTTF-TCNQ and HMTSF-TCNQ distort when transverse motion is coherent and an anisotropic three-dimensional band structure picture is appropriate.