The aniline dimer and trimer are investigated in their electronic ground state. The potential energy surface was thoroughly searched for low lying minima by applying global optimizations on a model potential, which is recalibrated on-the-fly by ab initio calculations (spin-component-scaled LMP2) at relevant configurations. The most stable structure of the dimer corresponds to a head-to-tail arrangement with both aniline monomers being nearly equivalent. DFT-SAPT calculations reveal that the interaction energy is dominated by van der Waals dispersion, which is of comparable size as for the benzene dimer, but with a much larger total interaction energy than for the latter. The global minimum of the aniline trimer corresponds to a hydrogen bonding arrangement involving three directional NH-N hydrogen bonds, with the individual monomers being clearly distinguishable. Nonadditive three-body dispersion contributions appear to play a minor role for the trimer.

The S1(pi*<--pi) state surfaces of the phenol-water(1

The potential energy surfaces of the S(0) and S(1)(pi(*)<--pi) states of the 2-naphthol(H(2)O)(n), n is an element of {1,2} clusters were explored at the level of coupled cluster (CC2) response theory. In the electronic ground state two different types of hydrogen-bonding networks coexist for n=2, (i) a cyclic one [similar to those of the water trimer and phenol(H(2)O)(2)] where the hydroxy group of the aryl alcohol acts simultaneously as H donor for the first, and as H acceptor for the second water molecule, and (ii) a hydrogen-bonding arrangement where the aromatic pi system is taking over the role as H acceptor. In the S(1) state, on the other hand, the cyclic conformers are unstable. Consequently, the first group of cyclic ground state conformers gives rise to broad unstructured band shapes in the absorption spectrum, whereas the second group of conformers involving the aromatic pi system gives rise to nicely structured band shapes. Based on these results the puzzling absorption spectrum of the n=2 cluster can properly be interpreted.

The lowest electronically excited states of the aniline dimer and trimer related to the lowest π(∗)←π transition of the monomer are investigated by applying time-dependent coupled cluster theory, primarily at the level of the (spin-component-scaled) CC2 model. Minimum energy structures in the vicinity of the Franck-Condon points were determined on the individual potential energy surfaces. For the dimer we find an excimer and a head-to-tail configuration (with the monomers substantially displaced relative to the ground state minimum) for the lowest (dark) and second lowest (bright) states, respectively. The excitation is delocalized on both chromophores for both of these states. For the trimer three distinct minima with quite different hydrogen-bonding arrangements are found for the three lowest states. In strong contrast to the dimer the excitation here is clearly localized on the individual aniline chromophores for each of these three states. One of the three geometries is rather similar to the ground state minimum, while the two others are rather different and thus have presumably quite small Franck-Condon factors. It can be expected that only the electronic origin of the first conformer can eventually be detected in the absorption spectrum of the trimer, provided that it is separated by high-enough barriers from other, energetically lower configurations.

Phosphorus sulfide cages alpha-P(4)S(4), alpha-P(4)S(5), beta-P(4)S(5), and beta-P(4)S(6) and transition-metal chlorides TaCl(5) and NbCl(5) form molecular adducts in CS(2)/n-hexane. The crystal structures of the adducts (TaCl(5))(alpha-P(4)S(4)), (TaCl(5))(alpha-P(4)S(5)), (TaCl(5))(beta-P(4)S(5)), (NbCl(5))(beta-P(4)S(5)), and (TaCl(5))(beta-P(4)S(6)) are reported and their conformation and energetic stability are discussed on the basis of ab initio electronic structure calculations. Furthermore bond lengths of coordinated and noncoordinated phosphorus sulfide cages obtained from experiment and theory are compared, emphasizing the changes within the cages that emerge upon coordination.