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The excited-state dynamics of the pure naphthalene clusters and of the mixed clusters involving two naphthalenes solvated with durene have been investigated as a function of the excess vibrational energy of the initially excited clusters. All of the clusters studied exhibit excimer fluorescence, depending strongly on the excess vibrational energy and on the solvation number. The isomerization rate has been measured by detecting a buildup in the excimer fluorescence and used as a probe of the cluster geometry. The trimer requires an excess energy of 870 cm−1 to promote the excimer formation with a rise time of 32 ns, suggesting a structurally less favorable process. The dimer and tetramer undergo rapid isomerization at much lower energies. The solvent addition is found to impede excimer formation, due to geometry restriction. The singly solvated cluster exhibits an excimer evolution time as slow as 60 ns.

First-principles electronic structure calculations based on the full-potential linear-muffin-tin-orbital method have been employed to study the contrasting effects of boron and hydrogen on the electronic structure of the I.lz ordered intermetallic Ni3Al. The total energy, the siteand I-projected densities of states, and the impurity-induced charge-density characteristics are calculated for various impurity configurations, to investigate the effects of local environment on the electronic structure. Total-energy calculations show that both boron and hydrogen impurities prefer to occupy octahedral interstitial sites that are entirely coordinated by six nickel atoms. Our results suggest that the underlying mechanism of the boron-induced strengthening in Ni3Al is the Ni-d and B-p hybridization between the nearestneighbor nickel and boron sites. This results in an enhancement of the intraplanar metallic bonding between the nickel atoms, an enhancement of interstitial bonding charge, and reduction of the bondingcharge directionality around the Ni atoms on the (001) NiAl planes. In contrast, hydrogen is found to enhance the bonding-charge directionality near some Ni atoms and to reduce the interstitial charge, suggesting that it promotes poor local cohesion. When both boron and hydrogen are present in Ni3Al, the dominant changes in the electronic structure are induced by boron and the charge distribution resembles that of Ni3Al+B. These results are broadly consistent with the notion of boron as a cohesion enhancer and hydrogen as an embrittler.

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