A novel method, designated as the density functional theory/coupled-cluster with single and double and perturbative triple excitation [DFT/CCSD(T)] correction scheme, was developed for precise calculations of weakly interacting sp(2) hydrocarbon molecules and applied to the benzene dimer. The DFT/CCSD(T) interaction energies are in excellent agreement with the estimated CCSD(T)/complete basis set interaction energies. The tilted T-shaped structure having C(s) symmetry was determined to be a global minimum on the benzene-dimer potential energy surface (PES), approximately 0.1 kcal/mol more stable than the parallel-displaced structure. A fully optimized set of ten stationary points on the benzene-dimer PES is proposed for the evaluation of the reliability of methods for the description of weakly interacting systems.

The interaction of the water molecule with benzene, polycyclic aromatic hydrocarbons, graphene, and graphite is investigated at the density-functional/coupled-cluster (DFT/CC) level of theory. The accuracy of the DFT/ CC method is first demonstrated by a comparison of the various interaction energies on the potential energy surface of water-benzene, water-naphthalene, and water-anthracene complexes with the data calculated at the coupled-cluster level at the basis set limit. The potential energy surface of water-graphene and water-graphite is relatively flat with diffusion barriers of about 1 kJ/mol. The structure with both hydrogen atoms of water pointing toward the graphene plane (denoted as a circumflex structure) above the center of the six-member ring is the global minimum characterized with an electronic interaction energy of -13 and -15 kJ/mol for graphene and graphite, respectively. The OH · · · π complexes (with one OH pointing toward the surface and the other OH being oriented along the surface) are up to 2 kJ/mol less stable than the circumflex complexes of water on graphene/graphite, depending on the position of the oxygen atom.

A combined experimental-computational approach was used to study the self-organization and microenvironment of 1-methylnaphthalene (1MN) deposited on the surface of artificial snow grains from vapors at 238 K. The specific surface area of this snow (1.1 × 10(4) cm(2) g(-1)), produced by spraying very fine droplets of pure water from a nebulizer into liquid nitrogen, was determined using valerophenone photochemistry to estimate the surface coverage by 1MN. Fluorescence spectroscopy at 77 K, in combination with molecular dynamics simulations, and density functional theory (DFT) and second-order coupled cluster (CC2) calculations, provided evidence for the occurrence of ground- and excited-state complexes (excimers) and other associates of 1MN on the snow grains' surface. Only weak excimer fluorescence was observed for a loading of 5 × 10(-6) mol kg(-1), which is ∼2-3 orders of magnitude below monolayer coverage. However, the results indicate that the formation of excimers is favored at higher surface loadings (>5 × 10(-5) mol kg(-1)), albeit still being below monolayer coverage. The calculations of excited states of monomer and associated moieties suggested that a parallel-displaced arrangement is responsible for the excimer emission observed experimentally, although some other associations, such as T-shape dimer structures, which do not provide excimer emission, can still be relatively abundant at this surface concentration. The hydrophobic 1MN molecules, deposited on the ice surface, which is covered by a relatively flexible quasi-liquid layer at 238 K, are then assumed to be capable of dynamic motion resulting in the formation of energetically preferred associations to some extent. The environmental implications of organic compounds' deposition on snow grains and ice are discussed.

The physical adsorption of molecules (C(2)H(2), C(2)H(4), C(2)H(6), C(6)H(6), CH(4), H(2), H(2)O, N(2), NH(3), CO, CO(2), Ar) on a graphite substrate has been investigated at the DFT/CC level of theory. The calculated DFT/CC interaction energies were compared with the available experimental data at the zero coverage limit. The differences between the DFT/CC results and experiment are within a few tenths of kJ mol(-1) for the most accurate experimental estimates (Ar, H(2), N(2), CH(4)) and within 1-2 kJ mol(-1) for the other systems (C(2)H(2), C(2)H(4), C(2)H(6), C(6)H(6), CO, CO(2)). For water-graphite and ammonia-graphite complexes, DFT/CC predicts interaction energies of 13 kJ mol(-1) in good accord with the DF-DFT-SAPT and DFT-D calculations. The relevance of the results obtained with the coronene model for the description of the physisorption on graphite surface was also studied.