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Manuscript Title: Electron scattering from quasi one-electron targets: experimental observables versus theoretical scattering amplitudes.
Authors: K. Bartschat, N. Andersen
Program title: ALKALI-OBSERVABLES
Catalogue identifier: ACVN_v1_0
Distribution format: gz
Journal reference: Comput. Phys. Commun. 84(1994)335
Programming language: Fortran.
Computer: VAX 4000-600.
RAM: 374K words
Word size: 64
Peripherals: disc.
Keywords: Electron, Scattering, Atomic physics, Inelastic, Superelastic, Excitation, Atomic hydrogen, Alkali atoms, Ls-coupling, Spin polarization, Light polarization, Orientation and, Alignment, Electron-photon Coincidences, Non-linear equations.
Classification: 2.4.

Nature of problem:
This program calculates a large number of observables that have been defined in the literature for both unpolarized and spin polarized electron impact of atomic hydrogen or quasi one-electrons atoms and ions [1,2]. Given partially complete experimental data for some of these observables, the code can be used to "invert" these data and obtain the scattering amplitudes - up to some ambiguities which can, however, be resolved with some confidence by comparing with accurate theoretical results.

Solution method:
Scattering amplitudes are read from disk and transformed from the "collision" to the "natural" coordinate system where the quantization axis is perpendicular to the scattering plane. Bilinear combinations of these amplitudes are then constructed to give various experimentally observable parameters. For an "almost complete" set of experimental data (that can be obtained with present experimental setups), an inversion algorithm is applied to produce several sets of scattering amplitudes that are consistent with such input data. If the theoretical results are sufficiently accurate, the "true" solution may be distinguished from the "ghosts" by comparing the various possibilities with the known theoretical solution.

Restrictions:
The code is currently restricted to transitions between atomic S states with even parity and P states of odd parity in light (quasi) one- electron systems. It is assumed that relativistic effects can be neglected during the collision, i.e. the scattering amplitudes (input data) have been calculated in a non-relativistic LS-coupling approximation.

Unusual features:
None.

Running time:
Since the manipulation of the input data for a straight calculation of the various observables is very fast, the running time depends mainly on the number of points (and therefore the accuracy) used in the search for crossings of the curves defined by the non-linear equations. With 2000 points (more than sufficient in most cases) spread in equal steps over the region where physical solutions may exist, the test run took 25 seconds on a VAX 4000-600.

References:
[1] N. Andersen, J.W. Gallagher and I.V. Hertel, Phys. Rep. 180, 1(1988)
[2] N. andersen and K. Bartschat, Comments At. Mol. Phys. 29, 157 (1993)