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Manuscript Title: A program for computing level crossings and the Back-Goudsmit effect.
Authors: P. Violino
Program title: BACK-GOUDSMIT
Catalogue identifier: ACRD_v1_0
Distribution format: gz
Journal reference: Comput. Phys. Commun. 4(1972)128
Programming language: Fortran.
Computer: IBM 360/75.
Operating system: OS, CMS.
RAM: 7K words
Word size: 32
Keywords: Atomic physics, Zeeman effect, Back-goudsmit effect, Paschen-back effect, Hyperfine structure, Structure fine, Level crossings, Radiofrequency Transitions.
Classification: 2.1.

Revision history:
Type Tit le Reference
correction 000A CORRECTION 27/1/77 See below

Nature of problem:
Several techniques of atomic spectroscopy, like h.f.s. measurements, level crossings, Hanle effect (when the h.f.s. is of the order of the width of a level), all require a precise knowledge of the positions of the sublevels of a fine or hyperfine multiplet as functions of the applied magnetic field. When the quantum numbers I and J (or S and L, according to the representation which is being used) are larger than a half, this requires the solution of the secular equation. This is carried out by this computer program, which can compute as well the positions of the level crossings between specified levels.

Solution method:
The solution is carried out by computing the secular matrix from the input data and then diagonalizing it. The positions of the level crossings are computed by an iterative procedure.

Restrictions:
The program is designed to handle quantum numbers l and j(or S and L) whose sum does not exceed 7. It can be easily extended to higher values by changing a few FORMAT statements.

Unusual features:
The program contains a few diagnostic features that alert the user when- ever his requirements are not compatible with the physical nature of the problem. Owing to its short computation time, the program can easily be used to evaluate the A and B hfs couping constants from an experimental set of level-crossing positions by an interpolation method.

Running time:
Compilation time is about 9 s, assembling and loading time is about 1 s, and execution time of the test run is about 4 s, on the 360/67 computer CNUCE.

CORRECTION SUMMARY
Manuscript Title: A program for computing level-crossings and the Back-Goudsmit effect. (C.P.C. 4(1972)128).
Authors: P. Violino
Program title: 000A CORRECTION 27/1/77
Catalogue identifier: ACRD_v1_0
Distribution format: gz
Journal reference: Comput. Phys. Commun. 13(1977)137
Classification: 2.1.