Quantum Dynamics of Coupled Large Amplitude Intermolecular Motions in Hydrogen-Bonded and Rare-Gas Heteroclusters

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Professor Zlatko Bacic of New York University is being supported by theTheoretical and Computational Chemistry program. The project aims to provide an accurate quantum mechanical description of the large amplitude intermolecular vibrations and the intermolecular potential energy surfaces of two hydrogen-bonded clusters, benzene-(H2O)n and (H2O)n, as well as the ultraviolet photodissociation of H2O in argon clusters and other rare gas matrices. An efficient quantum 6D method will be developed for the calculation of excited 6D intermolecular vibrational eigenstates of a broad class of complexes between a large aromatic molecule (e.g., benzene, naphthalene) and a small polyatomic molecule such as H2O, NH3. Vibrationally averaged structures and quantum tunneling dynamics of larger benzene-water clusters will be explored using a rigid-body quantum Monte Carlo method. A methodology for n-dimensional quantum calculation of the torsional energy levels and far-infrared spectra of small (H2O)n (n=3-6) clusters will be developed and extended to other intermolecular vibrations of the clusters. Bound state calculations of water and deuterated water clusters will characterize their torsional vibrational dynamics, quantum number assignments, and vibrationally averaged rotational constants. Photodissociation of H2O in Ar_nH2O (n=1-12,54) clusters and rare-gas matrices will be studied to gain an understanding of the mechanisms by which the solvent modifies the photo-fragmentation dynamics of a polyatomic solute (H2O), relative to that of the isolated gas-phase molecule. The photodissociation dynamics will be simulated using classical trajectories, whereas the initial conditions will be generated from the quantum 6D intermolecular eigenstates of the argon-water cluster in the ground electronic state. A quantitative understanding of the properties of, and processes in, water and aqueous solutions ultimately depends on the detailed knowledge of the water-water, water-solute, and solute-solute interactions. The quantum calculations of Professor Bacic for benzene-water and simple water clusters are a tool for the determination of their intermolecular potential energy surfaces from high-resolution spectroscopic data. These multidimensional potentials should allow characterization on a molecular level of liquid water and water-benzene, systems which are of fundamental and practical importance. In addition, a deeper understanding will be gained of the intricate dynamical properties of complex hydrogen bonding networks, which shape the properties of condensed phases and biologically important macromolecules.