Rate coefficients for state-to-state rotational transitions in CO induced by both para-and ortho-H 2 collisions are presented. The results were obtained using the close-coupling method and the coupled-states approximation, with the CO-H 2 interaction potential of Jankowski & Szalewicz (2005). Rate coefficients are presented for temperatures between 1 and 3000 K, and for CO(v = 0, j) quenching from j = 1 − 40 to all lower j ′ levels. Comparisons with previous calculations using an earlier potential show some discrepancies, especially at low temperatures and for rotational transitions involving large |∆j|. The differences in the well depths of the van der Waals interactions and the anisotropy of the two potential surfaces lead to different resonance structures in the energy dependence of the cross sections which influence the low temperature rate coefficients. Applications to far infrared observations of astrophysical environments are briefly discussed.

The structural evolution of small copper clusters of up to 15 atoms and the dissociative chemisorption of H2 on the minimum energy clusters are studied systematically using density functional theory. The preferred copper sites for chemisorption are identified and the transition state structures and activation barriers for clusters four to nine atoms are determined and found to be inconsistent with the empirical Bronsted-Evans-Polanyi relationship. The physicochemical properties of the clusters are computed and compared with the bulk and surface values. The results indicate that a phase transition must occur in the going from cluster to bulk.

We present a simple cluster model to understand the dissociative chemisorption of molecular hydrogen and the desorption of atomic hydrogen on platinum small clusters using the gradient-corrected density functional theory. Successive H 2 decomposition and sequential H desorption on the selected Pt n (n ) 2-5, 7-9) clusters were systematically studied, and the H 2 dissociative chemisorption energies and the H desorption energies at the full H saturation were identified. The reaction processes are driven by charge transfer from Pt atoms to H atoms assisted by strong orbital overlaps between Pt 5d orbitals and H 1s orbital, which leads to electron delocalization in large clusters of metal hydrides. It was found that the number of H atoms chemisorbed on the small Pt clusters increases almost linearly with the size of the selected Pt cluster.