E J Mansky

Empirical and semiempirical interaction potentials for rare gas–rare gas and rare gas–halide systems

The Tang–Toennies (TT) semiempirical model potentials for ion–atom systems is applied to the rare gas–halide negative ion exciplexes. The coefficients defining the repulsive Born–Mayer term in the TT semiempirical potentials are determined from the equilibrium bond length Re and dissociation energy De taken from ab initio calculations and from transport studies of these molecular ions. The damped dispersion and induction energy terms in the TT potentials are obtained from coupled Hartree–Fock calculations for the neutral rare gas atoms and F− and Cl− ions. The multipole polarizabilities for the heavier halogen atomic negative ions are estimated from a knowledge of polarizability ratios across isoelectronic sequences. The resultant semiempirical ionic potentials are compared to available ab initio calculations and the results of inversion of transport theory. To facilitate the comparison of the (sparse) ab initio data with the semiempirical potentials, a simple fitting procedure is presented for determinin...

Termolecular recombination at low gas density: Strong collision, bottleneck, and exact treatments

On introducing the probabilities for association as a function of internal separation R and internal energy E of the associating (A–B) species the strong collision model is thoroughly investigated and compared, as a case study, with the exact treatment of termolcular ion–ion recombination at low gas densities. A bottleneck model is also investigated. Analytical expressions for the one way equilibrium energy‐change rates at fixed R are provided in the Appendix.

The multichannel eikonal theory of electron-hydrogen collisions: I. Excitation of H( 1s)

The integral and differential cross sections for the electronic excitation of the 2l and 3l states of hydrogen obtained by the multichannel eikonal theory in a 10-channel basis are reported. The lambda , R and I parameters for the 2p state of hydrogen at 54.40 and 350 eV are also provided. Good agreement with the experimental data of Mahan et al. (1976) for the integral cross sections sigma 1s to 3l is achieved by the updated and extended multichannel eikonal theory. Two general conclusions follow from the results reported in the paper: (a) the first Born results underestimates experiment in s to d transitions and (b) indirect coupling mechanisms for the excitation of the 3d state of hydrogen are important and cannot be neglected. These conclusions indicate that the pseudostate basis used in a number of optical potential model calculations needs further refinement in the intermediate energy region.

The multichannel eikonal theory of electron-helium collisions. I. Excitation of He(11S)

Calculations of the integral and differential cross sections for the electronic excitation of the 21L and 31L states of helium are reported. The multichannel eikonal theory employing a 10-channel basis set is used. The lambda and chi parameters for the 21P and 31P states at 80 eV are also reported. A number of misprints concerning the original multichannel eikonal theory results of Flannery and McCann (1975) have occurred in the literature. These misprints are corrected in the paper. A detailed description of both the theoretical and experimental difficulties involved in the determination of the integral cross sections sigma 11S to 31S and sigma 11S to 31D is provided. In addition, a critique of the assumptions made in previous experimental determinations of the differential cross sections (both composite and magnetic sublevel) for the 21L states of helium is given. A principal conclusion of the paper is that the first Born approximation underestimates experimental data in the intermediate energy region for 1S1D transitions, in contrast to the trend seen in 1S1P transitions. In the paper the importance of indirect mechanisms in the excitation of the 31S and 31D is shown, thereby confirming the early results of Chung and Lin (1968, 1969) and the tentative conclusions of Massey (1969, 1974).

Termolecular recombination: Coupled nearest‐neighbor limit and uncoupled intermediate levels limit

Two extreme limits of collisional coupling in termolecular recombination are investigated. The coupled nearest neighbor (CNN) limit includes only couplings between neighboring excited energy levels of the associating species AB*, while the uncoupled intermediate levels (UIL) limit includes only couplings between the fully dissociated reactants A+ and B− and each of the (assumed uncoupled) excited levels of AB*, which are then coupled to the fully associated products AB. Comparison is made with results of previous exact and diffusion treatments.

The multichannel eikonal theory program for electron-atom scattering

Abstract The operation of the code MET_cross for the solution of the semiclassical multichannel eikonal theory for electron-atom scattering is described. Also described is a second code, MET_states, which utilizes the results produced by MET_cross to generate a complete set of state multipoles and coherence and alignment parameters needed to characterize the polarization properties of the radiation emitted in the decay of the metastable atomic states excited in the collision. Included also is a discussion of the relationship between the present codes used to solve the semiclassical multichannel eikonal theory and codes used to implement other semiclassical and quantal scattering theories of electron-atom scattering.

Automatic generation of analytical matrix elements for electron-atom scattering

Abstract A code which can be used to automatically generate entire sets of analytical matrix elements of the instantaneous electrostatic interaction potential between the projectile electron and the target atom is described. The code can be used at present for both hydrogen and helium target atoms. In the case of hydrogen, the present code Vij generalizes and extends an earlier code of Jamison [1]; while in the case of helium, Hartree-Fock frozen-core wave-functions are used to represent the two-electron wavefunctions. When an entire set of matrix elements is generated, a complete set of FORTRAN subroutines is produced which can be directly incorporated into the code MET_cross used to solve the multichannel eikonal theory (see accompanying paper). A principal application of the code Vij is to aid the elucidation of the systematic trends observed in transitions among metastable states in electron-atom collisions by studying the functional form of the underlying interaction matrix elements.

Electron-metastable-helium differential and integral cross sections

The differential and integral cross sections for the excitation of the 23P and the 33L (L identical to S, P and D) states of He from the metastable 23S state are calculated using the semiclassical multichannel eikonal theory with a nine-channel basis set. Comparison is made with the recent experimental results of Muller-Fiedler et al. (1984) and Rall et al. (1989) for the differential and integral cross sections, respectively. The agreement between the present multichannel eikonal results and the experimental data for the 33S and 33D differential cross sections is satisfactory. However, significant differences are noted between the experimental data and the present multichannel eikonal theory for the 23S to 23P, 33P differential cross sections.

Polarization fractions for the 21P, 31P and 31D states of helium

The polarization fractions for the 21P, 31P and 31D states of helium, determined from a 10-channel semiclassical eikonal calculation, are compared with a recent first-order many-body theory calculation of Csanak et al. (1989), and with experiment. A number of interesting points on the importance of channel coupling effects on the polarization fractions for the 21P, 31P and 31D states of He are addressed.

The issue of basis set size in e-+H(1s to 2s,2p) collisions

The results of the multichannel eikonal theory and three close-coupling calculations are compared for the sigma 1s to 2s and sigma 1s to 2p integral cross sections at intermediate energies. Also, the predictions of the three-state close-coupling theory of Kingston et al. (1976,1980,1982) and the present multichannel eikonal theory results for the moduli and phase angles of the complex scattering amplitudes for the 2p0 and 2p+1 substates of H at 54.40 eV are compared. Good agreement is obtained between the results of Kingston et al. and the results for the phase angles of the scattering amplitudes of both substates at small scattering angles. However, differences are noted in the modulus of the scattering amplitude of the 2p+1 substate at small scattering angles between the two theories. The implications this difference has on the composition and size of the basis sets used are addressed.