Vo Ky Lan

Cross sections calculations for electron oxygen scattering using the polarized orbital close coupling theory

The formulation given by Feautrier et al. (1971) for transitions induced by electron impact among ground state terms of atoms with one configuration npq is used with a slight modification by taking into account the orthogonality of the free wavefunction to the bound npq orbitals. A system of coupled integro differential equations, obtained from a modified close coupling expansion by including long range pseudo states, is solved numerically for electron incident on oxygen in the threshold region. The present results agree very closely with experiment. Independently of the evident astrophysical interest of these results (especially the excitation cross sections of the forbidden lines), the generalizations of such calculations to other systems with the same type of configuration is straightforward with this automatic code. The multichannel photodetachment cross sections of O- by dipole length and velocity formulae are also reported and discussed.

Atomic polarizabilities and polarized pseudo-states in the multiconfigurational approach. II. First row atoms and ions

For pt.I see ibid., vol.9, p.1065 (1976). Mean static dipole polarizabilities are calculated for the ground states of neutral and singly ionized atoms from Be to Ne. The polarizability is expressible in terms of the second-order energy correction in a formalism with the static dipole field being treated as a perturbation. The radial functions used in the calculation are determined by treating this second order energy as a variational functional, rather than by using the unperturbed atom variational principle. Because of this, the use of quite simple wavefunctions gives results which compare well with the much larger-scale calculations also performed.

The variable-phase method in multichannel electron-atom or electron-ion scattering

The variable-phase method is used to transform the system of second-order linear differential equations occurring in the outer region of electron-atom scattering problems (r>ra, where all exchange potentials can be neglected) into a system of first-order non-linear differential equations. The problem reduces to the direct outwards integration of the desired reactance K matrix, from its value given at r=ra by application of the R-matrix method in the inner region. The method is tested on various multichannel scattering processes (C+e-, C3++e-, N++e-,...) in the resonant or non-resonant region, when all channels are open or some of them are closed, and with up to 17 channels.

Accurate representation of molecular electrons by a few potential-adapted partial waves

Screening by the centrifugal field condenses the effect of molecular anisotropy into a few channels of the single-centre adiabatic partial-wave expansion of the low-energy scattered electron wavefunction. Applications to e+N2 and e+HCl are discussed.

The photoionization of neutral aluminium

The R-matrix method is used to calculate the photoionization cross section of ground state aluminium atoms Al(2P0), leaving the residual ions in their ground Al+(1Se) or first two excited states Al+(3P0,1P0). The initial bound state Al(2P0) as well as the three possible final continuum states (Al++e-)(2Se,2Pe, 2De) are represented consistently by R-matrix expansions in terms of three lowest states of the ion Al+(1Se,3P0,1P0). These ionic states are in turn described by accurate configuration-interaction wavefunctions. Good agreement is obtained with recent experiments by Kohl and Parkinson (1975) and by Esteva (1974) and results probably accurate to better than 15% are given from 2070 AA to 570 AA.

Atomic polarizabilities and polarized pseudo-states in the multiconfigurational approach. I. Theory and application to C, N and O

The determination of polarized pseudo-states for a complex atom using LS coupling is considered. These pseudo-states are obtained by solving variationally the Schrodinger equation for the unperturbed atom and the inhomogeneous first-order perturbation equation within a superposition-of-configurations framework. This technique, which can be easily applied to any state including excited states, allows the explicit introduction of electron correlation effects in a consistent way. The pseudo-states are generated primarily for use in negative-ion and electron-atom collision calculations but they also allow accurate polarizabilities and shielding factors to be evaluated. These are calculated for C, N, and O and the results compared with those obtained from other elaborate multiconfigurational techniques.

Photoionization of ground-state nitrogen atoms

The R-matrix theory of photoionization described by Burke and Taylor (1976) is used to obtain cross sections for the photoionization of ground-state nitrogen atoms. The calculations couple all channels corresponding to the 2s22p2 and 2s2p3 configurations of the residual ion. The results obtained are in excellent agreement with experiment.

R-matrix calculations for electron-molecule scattering

Abstract An R -matrix theory of electron scattering by diatomic molecules [1], in which the continuum wavefunction is expanded in a multicentred analytic basis, is applied to the scattering of low energy electrons by molecular hydrogen and nitrogen within the static-exchange approximation. Calculations are also reported for low energy scattering by atomic hydrogen and helium in order to demonstrate the effectiveness of the theory and the computer codes which are being developed [2]. The results prove very promising for the further application of the R -matrix method to more elaborate calculations on electron-molecule systems.

The method of polarized orbitals. II. The close coupling method using a polarized orbital expansion

For Pt. I, see ibid., vol.4, 658 (1971). A modified close coupling method is proposed using an expansion of the total wavefunction in the polarized target orbitals in order to take fully into account the polarizabilities of all the states which are retained in the expansion, and consequently of the long range electron interaction. This multichannel polarized orbital theory is a way to improve the results for elastic and inelastic scattering at low energies and is particularly appropriate to the study of excited states near threshold.

The photoionisation of the 4S0 ground state of atomic nitrogen

Photoionisation of the nitrogen ground state N(2s22p3 4S0) has been extensively studied starting from an accurate physical model. The initial bound state N(4S0) and the final continuum state N++e-(4Pe) are described consistently by collisional R-matrix-type expansions over the five parent ionic states N+(2s22p2 3Pe; 2s2p3 5S0, 3D0, 3P0, 3S0), represented in turn by accurate configuration interaction wavefunctions. An exact account of the couplings between the photoejection of the 2p and 2s valence electrons is essential in the low-energy spectrum, dominated by wide resonant structures. Close agreement with a recent high-resolution measurement of the strongest resonances contributes towards an assessment of the accuracy of the calculation. Detailed graphs and tables provide all the relevant information-total and partial cross sections, angular distribution of photoelectrons, analysis and fitting of prominent resonant structures-from the threshold at 852 AA ( approximately=1 Ryd) to 300 AA ( approximately=3 Ryd).