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Manuscript Title: CARS spectral profiles for homonuclear diatomic molecules.
Authors: W.M. Shaub, S. Lemont, A.B. Harvey
Program title: CARS
Catalogue identifier: AAHJ_v1_0
Distribution format: gz
Journal reference: Comput. Phys. Commun. 16(1978)73
Programming language: Fortran.
Computer: TI-ASC.
Operating system: 424.
RAM: 50K words
Word size: 32
Keywords: Molecular physics, Cars, Coherent anti-stokes Raman spectroscopy, Spectroscopy, Third-order Susceptibility, Nonlinear spectroscopy, Four wave mixing, Nonlinear optics, Laser physics, Electrical discharge.
Classification: 15, 16.2.

Nature of problem:
Raman spectra of molecules can be obtained with a much higher degree of sensitivity using Coherent Anti-Stokes Raman Spectroscopy (CARS). Calculations based on comparisons of experimental CARS data with computer-synthesized spectra are very useful for the determination of temperature and molecular concentrations in many engineering and scientific applications. These calculations are also invaluable to the basic understanding of the CARS process itself. Some of these important applications include the study of combustion systems and electrical discharges.

Solution method:
The program computes rotational and vibrational partition functions, populations, and the frequencies of all transitions allowed by selection rules for a given molecule under specified conditions. From these results and known spectroscopic constants, the square of the total third-order electric susceptibility, convoluted over a finite laser linewidth, is calculated as a function of frequency shift. This gives an adequate representation of the CARS spectral profile.

Restrictions:
The program currently performs calculations involving only homonuclear diatomic molecules. Straight forward modifications would be necessary if other types of molecules were to be considered. Furthermore, although the program can be used to calculate the O-, Q- and S-branches of the spectrum, it cannot calculate them simultaneously in an additive manner in its present form.