A single-valued double many-body expansion potential energy surface is reported for ground-state HCN based on a realistic representation of the long-range forces, and a fit to accurate ab initio calculations for the HCN↔CNH regions [J. M. Bowman, B. Gazdy, J. A. Bentley, T. J. Lee, and C. E. Dateo, J. Chem. Phys. 99, 308 (1993)] and novel full valence complete active space energies for CHN geometries. The various topographical features of the novel global potential energy surface are examined, and vibrational calculations are presented to characterize the minima associated to the HCN and CNH isomers. The quality of the new fit is compared with that of the seminumerical representation of Bowman et al. in terms of root-mean-squared deviations for stratified energy regimes.

An accurate single-sheeted double many-body expansion potential energy surface has been obtained for the ground electronic state of the hydrogen cyanide molecule via a multiproperty fit to ab initio energies and rovibrational data. This includes 106 rovibrational levels and 2313 discrete points, which are fit with a rmsd of 4 cm(-1) and 2.42 kcal mol(-1), respectively, and seven zero first-derivatives that are reproduced at three stationary points. Since the potential also describes accurately the appropriate asymptotic limits at the various dissociation channels, it is commended both for the simulation of rovibrational spectra and reaction dynamics.

Using a recently reported double many-body expansion potential energy surface, quasi-classical, statistical mechanics, and quantum resonance calculations have been performed for the HN 2 system by focusing on the determination of bimolecular (N + NH and H + N 2 ) and unimolecular (decomposition of HN 2 ) rate constants as well as the relevant equilibrium constants.

A single-valued double many-body expansion potential energy surface (DMBE I) recently obtained for the ground electronic state of the sulfur dioxide molecule by fitting correlated ab initio energies suitably corrected by scaling the dynamical correlation energy is now refined by fitting simultaneously available spectroscopic levels up to 6886 cm(-1) above the minimum. The topographical features of the novel potential energy surface (DMBE II) are examined in detail, and the method is emphasized as a robust route to fit together state-of-the-art theoretical calculations and spectroscopic measurements using a single fully dimensional potential form.

A dynamics study of the reaction Ar + HCN f Ar + H + CN for a wide range of initial vibrational and translational energies is reported. All calculations have been carried out with the quasiclassical trajectory method and a realistic potential energy surface for ArHCN. An attempt is made to reproduce the thermal rate coefficient for the reaction. Agreement with experiment is found to be good, and the limitations of the approach are stressed. A brief analysis of rotational effects, energy transfer, and unimolecular dissociation of highly excited HCN* molecules is also presented.

A single-sheeted double many-body expansion potential energy surface is reported for the lowest doublet state of HN2 by fitting additional multireference configuration interaction energies in the N...NH channel. A stratified analysis of the root-mean-squared error indicates an accuracy superior to that achieved for the previously reported form. Detailed dynamical tests are also performed for the N + NH reaction using both the quasi-classical trajectory method and the capture theory, and the results are compared with available empirical data. The vibrational resonances of the HN2 metastable radical are also calculated and compared with previous theoretical predictions.

An accurate single-valued double many-body expansion potential energy surface has been obtained for the ground electronic state of the sulfur dioxide molecule (SO 2) by fitting novel ab initio energies suitably corrected by scaling its correlation energy. The stationary points of the new surface have been exhaustively analyzed, and the quality of the fit was appreciated from the stratified root-mean-square deviations between the points and the analytical potential.

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