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Ab initio potential data at the CCSD(T) level of theory with an aug-cc-pVTZ basis was used for an accurate determination of potential energy surface. The resulting potential function is valid for all twelve vibrational degrees of freedom and a torsional reaction path was derived for this potential and then low lying vibrational levels of methanol were calculated by MULTIMODE.

A full-dimensional ab initio potential energy surface and dipole moment surface for water dimer are presented. The surfaces can dissociate into two water molecules correctly, with equilibrium dissociation energy D(sub e) = 1665.74 cm(super -1).

Argon predissociation spectroscopy is used to observe the first vibrational spectra of the OH(super -).H2O and Cl(super -).H2O complexes in the 1000--1900 cm(super -1) energy region. The extension to lower energy allows the exploration of the spectral signatures of the intramolecular bending fundamentals (v2) of the bound water molecule, as well as, in the strongly bond systems such as OH(super -).H2O, the motion of the shared proton.

An effort is made to obtain vibrational energies of H5O2(super +1) in full dimension, in this study. For this purpose, the diffusion quantum Monte Carlo method and the vibrational configuration interaction methods are used.

The correction of the statement about localization of the C[H.sub.5.sup.], as described in the 'Nature of the Chemical Bond in Protonated Methane', is illustrated along with a new assignment of the infrared spectrum. The analysis has concluded that the [H.sub.2.sup.+] stretch vibration cannot contribute to the observed intensity in the 2400 or 2700 [cm.sup.-1] region of the spectrum.

Two different methods are used to calculate the spectra of deuterated analogues to CH(sub 5)(super +) at various stationary points on the potential surface. The predicted spectra for CH4D(super +) and CHD4 contain features associated with the single D or H atom being preferentially located in one of the bonding sites.

An ab initio calculation of the potential surface, quantum structures, and zero-point energies of CH5(super +) and CH2D3(super +) in full dimensionality is presented. The diffusion Monte Carlo (DMC) calculations of the fully anharmonic zero-point energies and ground-state wave functions of CH5(super +) and CH2D3 (super +) uses the potential that obeys the permutational symmetry of five hydrogen atoms.

Realistic, full-dimensional calculations of vibrational energies of H5O2 are undertaken and the disappearance of the high frequency OH band for the Ar2 complex is examined. The findings indicate the high energy OH-vibrational band disappeares with two Ar atoms complexed to H3O2- instead of a single Ar atom.