  The MIRS software for the modeling of ro-vibrational spectra of polyatomic
molecules was considerably extended and improved. The original version
(Nikitin, et al. JQSRT, 2003, pp. 239--249) was especially designed for
separate or simultaneous treatments of complex band systems of polyatomic
molecules. It was set up in the frame of effective polyad models by using
algorithms based on advanced group theory algebra to take full account of
symmetry properties. It has been successfully used for predictions and data
fitting (positions and intensities) of numerous spectra of symmetric and
spherical top molecules within the vibration extrapolation scheme. The new
version offers more advanced possibilities for spectra calculations and
modeling by getting rid of several previous limitations particularly for the
size of polyads and the number of tensors involved. It allows dealing with
overlapping polyads and includes more efficient and faster algorithms for the
calculation of coefficients related to molecular symmetry properties (6C, 9C
and 12C symbols for C_{3v}, T_{d}, and O_{h} point groups) and for better
convergence of least-square-fit iterations as well. The new version is not
limited to polyad effective models. It also allows direct predictions using
full ab initio ro-vibrational normal mode hamiltonians converted into the
irreducible tensor form. Illustrative examples on CH_{3} D, CH_{4}, CH_{3} Cl,
CH_{3} F and PH_{3} are reported reflecting the present status of data
available. It is written in C++ for standard PC computer operating under
Windows. The full package including on-line documentation and recent data are
freely available at [http://www.iao.ru/mirs/mirs.htm] or
[http://xeon.univ-reims.fr/Mirs/||http://xeon.univ-reims.fr/Mirs/] or
[http://icb.u-bourgogne.fr/OMR/SMA/SHTDS/MIRS.html].
