PHYS 445 
Fulldimensional quantum investigations of (H_{2}O)_{2} vibrational levels and its Infrared spectra in gas phase have been carried out on recently reported fulldimensional ab initio potential energy and dipole moment surfaces. These computations are based on the code MULTIMODE, utilizing conventional singlereference VSCF/VCI calculations that are supplemented with Diffusion Monte Carlo (DMC) analysis. Single reference IR spectra first are computed by taking each of the ten lowenergy stationary points as reference of normal modes. The IR spectra are then synthesized based on their respective DMC statistical weights[Ref.1], i.e. the densities of zeropoint wavefunction around each configuration. A synthesized IR spectrum is presented in 0 – 4000 cm^{1}, comparing with experimental data. Sum of weights around the global minimum and two lowest saddle points is approximately 90%. Therefore, most IR bands in synthesized spectra can be interpreted with normal mode descriptions at these three configurations. Several absorption features around 1300 cm^{1}, 2200 cm^{1} and 3300 cm^{1} are tentatively assigned to the overtones or combinational bands of inter/intramonomer motions. Uncertainties of DMC weights and internal restrictions of current simulations are also discussed. We thank the Office of Naval Research and National Science Foundation for support.
Ref. 1: Huang, X.; Bowman, J. M.; McCoy, A. B.; Johnson, L. M.; Savage, C.; Dong F.; Nesbitt, D. J. Science, 2006, 311, 60.

Poster Session
7:30 PM10:00 PM, Wednesday, 13 September 2006 Moscone Center  Hall D, Poster
Division of Physical Chemistry 