Quantum simulations of water dimer IR spectra

PHYS 445

Xinchuan Huang1, Stuart Carter2, and Joel M. Bowman, jmbowma@emory.edu2. (1) NASA Ames Research Center, Moffett field, CA 94035, (2) Cherry L. Emerson Center of Scientific Computation and Department of Chemistry, Emory University, Atlanta, GA 30322
    Full-dimensional quantum investigations of (H2O)2 vibrational levels and its Infrared spectra in gas phase have been carried out on recently reported full-dimensional ab initio potential energy and dipole moment surfaces.  These computations are based on the code MULTIMODE, utilizing conventional single-reference 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 low-energy 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 zero-point 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/intra-monomer 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 PM-10:00 PM, Wednesday, 13 September 2006 Moscone Center -- Hall D, Poster

Division of Physical Chemistry

The 232nd ACS National Meeting, San Francisco, CA, September 10-14, 2006