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Manuscript Title: A Fortran program for the calculation of hyperfine structure and Stark effect in the rotational transition of a 2sigma diatomic molecule.
Authors: K.P.R. Nair
Program title: DBLSIG
Catalogue identifier: ACDC_v1_0
Distribution format: gz
Journal reference: Comput. Phys. Commun. 34(1984)163
Programming language: Fortran.
Computer: CYBER 175.
Operating system: NOS/BE 1.5.
RAM: 100K words
Word size: 60
Keywords: Molecular physics, Spectroscopy, Doublet sigma molecule, Microwave spectra, Hyperfine structure, Stark effect.
Classification: 16.2.

Nature of problem:
Calculation of hyperfine structure (magnetic and nulcear quadrupole) and Stark effect in open shell doublet sigma ground state diatomic molecule by the method of diagonalization of energy Hamiltonian.

Solution method:
The program builds up the energy matrices in terms of F which is the total quantum number of the angular momentum F= N + S + I1 and for the desired magnetic quantum number MF. N, S and I1 are the rotation, electric spin and nuclear spin angular momenta. The whole matrix is then diagonalized and the microwave transitions are printed out.

The dimensions of the matrices are in principle infinite. But a judicious choice can be made to reduce the dimensions to suit the computer memory according to the accuracy of the experimental measurement. If larger dimensions are needed this may be accomplished by changing the dimension and common statements accordingly. For the stark effect only the Pi-type (with selection rule Delta MF=0) are printed out. For Delta MF=+1 transitions (Sigma-transitions) the calculation should be repeated with different MF and the eigenvalues can be used.