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Manuscript Title: F.F.C.: A program for calculating Franck-Condon factors and R- centroids for transitions between the vibrational-rotational levels of two electronic states of a diatomic molecule.
Authors: M. Dagher, H. Kobeissi
Program title: F.F.C.
Catalogue identifier: ABBE_v1_0
Distribution format: gz
Journal reference: Comput. Phys. Commun. 47(1987)305
Programming language: Fortran.
Computer: IBM 3090.
Operating system: VM/SP HPO.
RAM: 70K words
Word size: 64
Peripherals: magnetic tape.
Keywords: Molecular physics, Diatomic molecule, Vibration-rotation, Franck-condon factors, R-centroids, Function wave, Overlap integral, Franck-condon integral, Canonical method, Analytic expression, Electronic states, Coupling coefficients, Normalization integral.
Classification: 16.3.

Nature of problem:
The program presents a new method for computing the Franck-Condon factors and the R-centroids for a diatomic molecule.

Solution method:
The canonical function method is used to calculate the wave function for each interval (rm, rm+1) of the axis r, in the form of a uniformly and absolutely convergent series. The computation of the Franck-Condon factor is then reduced so that of the "Franck-Condon integral" which can be also written in the form of a uniformly and absolutely convergent series in (rm, rm+1). The coefficients of this series are called "coupling constants" and depend uniquely on the eigenvalues E**a and E**b of the considered transition and of the potentials U**a and U**b.

Provided that the Born-Oppenheimer approximation is valid, there are no known restrictions.

Unusual features:

Running time:
Dependant upon the number of transitions to be calculated. 73 seconds for the first test run, 3 s for the second and 43 s for the third.