| This dissertation consists of three parts. Part I reports the Diffusion Monte Carlo (DMC) calculations of the intermolecular vibrational ground states of ArnHF clusters, on the best available pairwise additive potential energy surfaces (PESs) for n = 1--12, and on the high-quality non-additive PESs for n = 1--7 . The intermolecular degrees of freedom of the clusters are treated in full dimensionality. The calculations yield ground state energies, probability distributions of intermolecular coordinates and HF vibrational frequency shifts. The calculated frequency shifts, especially those obtained from the non-additive PESs, show excellent agreement with the available spectroscopic data and provide reliable predictions for future experimental studies.; Part II investigates the quantum solvation of the HF molecule by para-hydrogen molecules. The minimum-energy structures determined for n = 1--12 have all the H2 molecules in the first solvent shell. The first solvent shell closes at n = 12, resulting in an icosahedral solvent cage. The zero-point energy of (p-H2)nHF clusters calculated by DMC is unusually large relative to the potential well depth, making the solvent cage exceptionally fluxional. However, the characteristic features of the static minimum-energy cluster geometries are remarkably preserved and clearly recognizable from the pattern of the modulated H2 density around the HE The rigidity of the solvent clusters displays an interesting size dependence, reaching its maximum for n = 12, where the first solvent shell closes. The anisotropy of the solvent, very pronounced for small clusters, decreases rapidly with increasing n, so that for n ∼ 8--9 the solvent environment is practically isotropic.; Part III deals with the microscopic process where a small number of He atoms solvates the HCl dimer. The size evolution of the equilibrium cluster structures and of the highly quantum solvation dynamics are investigated using DMC. The results reveal that the first six helium atoms are delocalized within the equatorial ring centered in the middle of, and perpendicular to, the line connecting the centers of mass of the two HCl monomers. As more helium atoms are added, the helium density starts to spread beyond the central region of the dimer. The solvation effects on the interchange-tunneling dynamics of the HCl dimer are also discussed. |
