**Vladimir Tyuterev
**

Among various methods and theoretical models for calculation of high-resolution
molecular vibration-rotation spectra three most widespread types are to be considered:
a)'local' (effective) methods, based on the perturbation theory and on effective
Hamiltonians for sets of nearby vibrational states (polyads) accounting for strong rovibrational
resonance interactions within these polyads;
b) 'intermediate' version of calculations, which use vibration extrapolation scheme for
successive polyads;
c) 'global' methods (many of them use a variational technique) which allow to calculate
an entire set of rovibrational states and transitions up to the dissociation from molecular
properties; a potential energy surface (PES) is used to calculate energies and line positions and
dipole moment surfaces (DMS) are used to calculate line and band intensities.
Specific advantages and problems related with applications of these complementary
approaches to molecular spectroscopy and dynamics will be discussed. Recently accurate PES of
several triatomic molecules such as water[1], ozone[2,3] and H_{2}S[4] have been obtained using
extended ab initio electronic structure calculations or advanced empirical optimisation
accounting for spectroscopic and chemical information (barriers, dissociation limits etc.).
These surfaces were used to derive very accurate spectroscopic effective Hamiltonians for
polyads of rotation-vibrational states coupled by strong resonances through a systematic
application of quantum mechanical Contact Transformations [5] which have been programmed
[6] to high orders of the perturbation theory. This allows building systematic links among the
methods (a),(b),(c) and using information from complementary sources. Prospective of this
technique for study of intensity anomalies and isotopic effects [7], for interpretation of
spectroscopic parameters, for semi-classical PO analyses, and for assignments of excited states
near the dissociation limit observed in recent high-resolution experiments currently in progress at
the University of Reims with collaborations will be discussed.

**References**

1. H.Partridge, D.W.Schwenke, J.Chem. Phys. **106**, 4618 (1997).

2. Vl.G.Tyuterev, S.A.Tashkun, D.W.Schwenke, P.Jensen, T.Cours, A.Barbe and M.Jacon, Chem. Phys. Lett., **316**, 271 (2000 ).

3. R.Siebert, R.Fleurat-Lessard, R.Schinke, M.Bitterova, S.C.Farantos J. Chem. Phys., **116**, 9749 (2002).

4. Vl.G. Tyuterev , S.A.Tashkun , and D.W.Schwenke, Chem. Phys. Lett., **348**, 223 (2001).

5. Vl.G.Tyuterev, in 'Symmetry and perturbation theory' , World Scientific Publishing (2002).

6. Vl.G.Tyuterev, S.A. Tashkun, H.Seghir, HighRus-2003, SPIE Proceedings , 5311, 164 (2004).

7. Vl.G.Tyuterev, L.Regalia-Jarlot, D.W. Schwenke , S.A.Tashkun,Y.G.Borkov, C.R. Physique, **5**, 189 (2004).