Andrew N. Feldt

Exact inclusion of exchange in calculations of cross sections for vibrational excitation of N2 by low-energy electrons

Elastic and inelastic differential and integral cross sections for low-energy vibrational excitation of N2 by electron impact are calculated by solving vibrationally coupled scattering equations. Unlike previous calculations of this type, which used model-exchange potentials, the present formulation incorporates exchange effects rigorously. The resulting coupled integrodifferential equations are solved using a combination of linear-algebraic and R-matrix-propagator techniques. Theoretical differential cross sections for both resonant and non-resonant scattering are compared to recent absolute measurements by Allan (2005 J. Phys. B: At. Mol. Opt. Phys. 38 3655), with special attention given to the region of the 2Πg shape resonance near 2.4 eV and to disagreements between theory and experiment at non-resonant energies above this region.

Breakdown of the adiabatic-nuclear-rotation approximation for near-threshold e-H2 collisions

The validity of the adiabatic-nuclear-rotation theory of electron-molecule scattering is assessed for near-threshold rotational excitation of H2. Integrated and differential cross sections calculated using this theory are compared with those determined using the more accurate laboratory frame close-coupling theory. A recently proposed energy-modified adiabatic theory is tested and shown to lead to marked improvement in the approximate integrated (but not differential) cross sections.

Through scattering theory with gun and camera: Coping with conventions in collision theory

Four ambiguities are inherent in time-independent quantum-mechanical scattering theory: two in the normalization of continuum functions, and two in the relation between various scattering matrices. These ambiguities allow the use of different conventions in scattering theory. This freedom has led to inconsistencies among textbooks, monographs, review articles, and research papers. We identify these ambiguities, indicate their context and origin in scattering theory, give the key equations of scattering theory in a form that can by adapted to any convention, and show interrelations between these equations that can lead to confusion and error. We also give several diagnostic approaches for determining the conventions used in a particular source, and reference conventions adopted in widely used books on scattering theory.

Period variations in spectroscopic binaries - SS Cygni and AE Aquarii

The period variation (k) and orbital elements, such as the epoch period and radial velocity, are computed for the two spectroscopic noneclipsing binaries using data published by Walker and Chincarini (1968), and Smak (1969) for the SS Cygni and data from Chincarini and Walker (1980), and Joy (1954) for the AE Aquarii. The SS Cygni k value is significant to about a 5 standard deviation, while the AE Aquarii k value is significant to about 0.5 standard deviation. The various data are compared and the main characteristics of both binary systems are summarized.