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Manuscript Title: A code for analysis of the fine structure in near-rigid weakly-bonded open-shell complexes that consist of a diatomic radical in a 3Σ state and a closed-shell molecule
Authors: Wafaa Fawzy
Program title: TSIG_COMP
Catalogue identifier: AEGM_v1_0
Distribution format: tar.gz
Journal reference: Comput. Phys. Commun. 181(2010)1789
Programming language: Fortran 90, free format.
Computer: SGI Origin 3400, workstations and PCs.
Operating system: Linux, UNIX and Windows (see Restrictions below).
RAM: Case dependent
Keywords: Vibration-Rotation Spectra, Quantum Mechanical Calulation, Open-Shell Complexes.
Classification: 16.2.

Nature of problem:
TSIG_COMP calculates frequencies, relative intensities, and expectation values of the various quantum numbers and parities of bound states involved in allowed ro-vibrational transitions in semi-rigid planar weakly-bonded open-shell complexes. The complexes of interest contain a free radical in a 3Σ state and a closed-shell partner, where the electron-spin electron-spin interaction, electron-spin rotation interaction, and centrifugal forces significantly modify the spectral patterns. To date, ab initio methods are incapable of taking these effects into account to provide accurate predictions for the ro-vibrational energy levels of the complexes of interest. In the TSIG_COMP program, the problem is solved by using the proper effective Hamiltonian and molecular basis set.

Solution method:
The program uses a Hamiltonian operator that takes into account vibration, end-over-end rotation, electron-spin electron-spin and electron-spin rotation interactions as well as the various centrifugal distortion terms. The Hamiltonian operator and the molecular basis set are used to set up the Hamiltonian matrix in the inertial axis system of the complex of interest. Diagonalization of the Hamiltonian matrix provides the eigenvalues and the eigenfunctions for the bound ro-vibrational states. These eigenvalues and eigenfunctions are used to calculate frequencies and relative intensities of the allowed infrared or microwave transitions as well as expectation values of all the quantum numbers and parities of states involved in the transitions. The program employs the method of least squares fits to fit the observed frequencies to the calculated frequencies to provide the molecular parameters that determine the geometry of the complex of interest.

Restrictions:
The number of transitions and parameters included in the fits is limited to 80 parameters and 200 transitions. However, these numbers can be increased by adjusting dimensions of the arrays (not recommended).
Running the program under MS windows is recommended for simulations of any number of transitions and for fitting a relatively small number of parameters and transitions (maximum 15 parameters and 82 transitions), for fitting larger number of parameters run time error may occur. Because spectra of weakly bonded complexes are recorded at low temperatures, in most of cases fittings can be performed under MS windows.

Running time:
Problem-dependent. The provided test input for Linux fits 82 transitions and 21 parameters, the actual run time is 62 minutes. The provided test input file for MS windows fits 82 transitions and 15 parameters; the actual runtime is 5 minutes