Quasi-classical trajectory (QCT) calculations have been carried out to study the stereodynamics of the reactions H + LiH(+) (v = 0, j = 0) --> H(2) + Li(+) and H(+) + LiH (v = 0, j = 0) --> H(2)(+) + Li which proceed on the two lowest-lying electronic states of the LiH(2)(+) system, using the ab initio potential energy surfaces (PESs) of Martinazzo et al. [J. Chem. Phys., 2003, 119, 11241]. Differential cross sections (DCSs) and alignments of the product rotational angular momentum for the two reactions are reported. Though the two PESs employed in the current calculations have significant differences, the tendencies of the product rotational alignment are same on the whole, and some common features emerge. This interesting phenomenon probably indicates that, for this system, the characters of the PESs have a weak influence on the alignments of the products. The conclusion is confirmed by a further discussion of rotational alignment parameter which also indicates that the two PESs are repulsive, i.e., the exoergic processes of the reactions taking place on the exit valleys of the PESs.

Quasi-classical trajectory calculations have been performed on the adiabatically allowed reactions taking place on the two lowest-lying electronic states of the LiH 2 + system, using the ab initio understanding of the lithium chemistry in the early universe. Thermal rate constants for the above reactions have been computed in the temperature range 10-5000 K and found in reasonably good agreement with estimates based on the capture model.

Transition states and reaction paths for a hydrogen molecule dissociating on small aluminum clusters have been calculated using density functional theory. The two lowest spin states have been taken into account for all the Al(n) clusters considered, with n=2-6. The aluminum dimer, which shows a (3)Π(u) electronic ground state, has also been studied at the coupled cluster and configuration interaction level for comparison and to check the accuracy of single determinant calculations in this special case, where two degenerate configurations should be taken into account. The calculated reaction barriers give an explanation of the experimentally observed reactivity of hydrogen on Al clusters of different size [Cox et al., J. Chem. Phys. 84, 4651 (1986)] and reproduce the high observed reactivity of the Al(6) cluster. The electronic structure of the Al(n)-H(2) systems was also systematically investigated in order to determine the role played by interactions of specific molecular orbitals for different nuclear arrangements. Singlet Al(n) clusters (with n even) exhibit the lowest barriers to H(2) dissociation because their highest doubly occupied molecular orbitals allow for a more favorable interaction with the antibonding σ(u) molecular orbital of H(2).

The isotopic effects on stereodynamic properties for the title reactions occurring on the two lowest-lying electronic potential energy surfaces (PESs) of LiH(2)(+) are investigated in detail by means of the quasi-classical trajectory (QCT) method at a collision energy of 0.5 eV, using the ab initio potential energy surfaces (PESs) of Martinazzo et al. (J. Chem. Phys., 2003, 119, 11241). The corresponding reactions comprise: (i) H/D/T + LiH(+) --> HH/HD/HT + Li(+) and H + LiH(+)/LiD(+)/LiT(+) --> HH/HD/HT + Li(+); (ii) H(+)/D(+)/T(+) + LiH --> HH(+)/HD(+)/HT(+) + Li and H(+) + LiH/LiD/LiT --> HH(+)/HD(+)/HT(+) + Li. Differential cross sections (DCSs) and alignments of the product rotational angular momentum for all of these reactions are reported. The results illustrate that the reason for the abnormal behavior of the DCSs for the title reactions reported in the previous work is ascribed to the sensitive role of the projectile atomic mass, and indicate that the long-range interactions play a more important role than the mass factor in ion-molecule reactions. The current topic for this special mass combination system shows some new features of the stereodynamics differing from the previous studies for "typical" mass-combination reactions.

Recent years have witnessed an ever growing interest in theoretically studying chemical processes at surfaces. Apart from the interest in catalysis, electrochemistry, hydrogen economy, green chemistry, atmospheric and interstellar chemistry, theoretical understanding of the molecule-surface chemical bonding and of the microscopic dynamics of adsorption and reaction of adsorbates are of fundamental importance for modeling known processes, understanding new experimental data, predicting new phenomena, controlling reaction pathways. In this work, we review the efforts we have made in the last few years in this exciting field. We first consider the energetics and the structural properties of some adsorbates on metal surfaces, as deduced by converged, first-principles, plane-wave calculations within the slab-supercell approach. These studies comprise water adsorption on Ru(0001), a subject of very intense debate in the past few years, and oxygen adsorption on aluminum, the prototypical example of metal passivation. Next, we address dynamical processes at surfaces with classical and quantum methods. Here the main interest is in hydrogen dynamics on metallic and semi-metallic surfaces, because of its importance for hydrogen storage and interstellar chem- istry. Hydrogen sticking is studied with classical and quasi-classical means, with particular emphasis on the relaxation of hot-atoms following dissociative chemisorption. Hot atoms dynamics on metal surfaces is investigated in the reverse, hydrogen recombination process and compared to Eley-Rideal dynamics. Finally, Eley-Rideal, collision-induced desorption, and adsorbate-induced trapping are studied quantum mechanically on a graphite surface, and unexpected quantum effects are observed.