Search

The new results for the water dimer equilibrium constant, K(sub p)(T) in the range 190-390 K, using a flexible potential energy surface fitted to spectroscopical data are presented. The newly calculated values for K(sub p)(T) are in very good agreement with available experimental data at room temperature, and at higher temperatures, with the analysis of the convergence of the partition function reveals that quasi-bound states are likely to contribute to the equilibrium constant.

An extensive and detailed theoretical analysis of the electron charge displacement accompanying the interaction, over several crucial sections of the potential energy surface (PES) was performed to demonstrate that the water-H2 interaction is accompanied by charge transfer (CT) and that the observed stabilization energy correlates quantitatively with CT magnitude at all distances. CT is found to be a significant and strongl stereospecific component of the water-H2 interaction chemistry, with water functioning as electron donor or acceptor in different orientations.

TheD++ H2reaction is investigated by meansof a time independent quantum mechanical (TIQM) and statistical quantummechanical (SQM) methods. Differential cross sections and productrotational distributions obtained with these two theoretical approachesfor collision energies between 1 meV and 0.1 eV are compared to analyzethe dynamics of the process. The agreement observed between the TIQMdifferential cross sections and the SQM predictions as the energyincreases revealed the role played by the complex-forming mechanism.The importance of a good description of the asymptotic regions isalso investigated by calculating rate constants for the title reactionat low temperature. [ABSTRACT FROM AUTHOR]

Integral cross-section measurements for the system water—H2 in molecular-beam scattering experiments are reported. Their analysis demonstrates that the average attractive component of the water—H2 intermolecular potential in the well region is about 30% stronger than dispersion and induction forces would imply. An extensive and detailed theoretical analysis of the electron charge displacement accompanying the interaction, over several crucial sections of the potential energy surface (PES), shows that water—H2 interaction is accompanied by charge transfer (CT) and that the observed stabilization energy correlates quantitatively with CT magnitude at all distances. Based on the experimentally determined potential and the calculated CT, a general theoretical model is devised which reproduces very accurately PES sections obtained at the CCSD(T) level with large basis sets. The energy stabilization associated with CT is calculated to be 2.5 eV per electron transferred. Thus, CT is shown to be a significant, strongly stereospecific component of the interaction, with water functioning as electron donor or acceptor in different orientations. The general relevance of these findings for water's chemistry is discussed. [ABSTRACT FROM AUTHOR]

The H + HeH + → He + H 2 + reaction has been studied by means of a combination of theoretical approaches: a statistical quantum method (SQM), ring polymer molecular dynamics (RPMD), and the quasiclassical trajectory (QCT) method. Cross sections and rate constants have been calculated in an attempt to investigate the dynamics of the process. The comparison with previous calculations and experimental results reveals that despite the fact that statistical predictions seem to reproduce some of the overall observed features, the analysis at a more detailed state-to-state level shows noticeable deviations from a complex-forming dynamics. We find some differences in cross sections and rate constants obtained in the QCT calculation with a Gaussian binning procedure with respect to previous works in which the standard histogram binning was employed.

We present a new method taking explicitly into account the coupling between rotation and bending of a nonlinear triatomic molecule colliding with an atom. This approach based on a rigid-bender treatment of the triatomic molecule was originally developed for the case of triatomic molecule linear at equilibrium. It is here extended to the case of a colliding bent triatomic molecule at equilibrium and applied to the case of the para -H 2 + H 2 O inelastic collision using a new H 2 O- para -H 2 adiabatically reduced 4D potential. The results of the method for purely rotational transitions are compared to those of rigid-rotor calculations while vibrational quenching rates of the first exited bending level are calculated for the first time at the close-coupling level.