Quasiclassical and quantum calculations of dynamics of small molecules

The dynamics of several small molecules such as H5O2 + and H2C2 are examined and calculated in this dissertation.;We report quantum and quasiclassical calculations of proton transfer in the reaction H3O+ + H2O in three degrees of freedom. The reduced dimensional potential energy surface is obtained from the full dimensional OSS3(p) energy function of H5O2 + [L. Ojamae, I. Shavitt, and S. J. Singer, J. Chem. Phys. 109, 5547 (1998)]. This surface is used to obtain the zero total angular momentum cumulative reaction probability and cross sections. Comparisons of these quantities are made to assess the importance of quantum effects in this reduced dimensional reaction and the thermal rate constant is obtained.;We report quasiclassical trajectory calculations of the dynamics of the two reaction channels of formaldehyde dissociation on a global ab initio potential energy surface: the molecular channel H2CO → H2 + CO and the radical H2CO → H + HCO. For the molecular channel, it is confirmed that above the threshold of the radical channel an intramolecular hydrogen abstraction pathway is opened to produce CO with low rotation and vibrationally hot H2. The low-jCO and high-nuH2 products from the second pathway increase with the total energy. The results agree well with very recent velocity-map imaging experiments of Suits and coworkers and solves a mystery first posed by Moore and coworkers.;We report full-dimensional calculations of vibrational energies of trans-C2H2(A) using the code MULTIMODE and with a full-dimensional potential energy surface obtained by fitting "Coupled-Cluster-Singles-and Doubles" energies. The CCSD calculations were done with the code 'ACES'. We compare the properties of the surface to previous calculations at the trans-minimum and compare the vibrational energies to experiment.;We report a full dimensional ab initio-based global potential energy surface (PES) and dipole moment surface (DMS) for Cl - H2O. Both surfaces are invariant to hydrogen exchange. The PES is a fit to thousands of electronic energies calculated using the coupled-cluster method with a moderately large basis. The infrared spectrum and vibrational dynamics are reported and compared to experiment. Results for DOD and HOD/DOH are also presented.