Convergence testing of the analytic representation of an ab initio dipole moment function for water: Improved fitting yields improved intensities

In general, when computing intensities for polyatomics, one has to interpol ate the dipole moment function obtained from ab initio calculations. For so me high overtones of the water molecule, the computed intensities can be ve ry sensitive to the way in which the interpolation is done. Our previous an alytic representation [H. Partridge and D. W. Schwenke, J. Chem. Phys. 106, 4618 (1997)] was not adequate. We show that stable results can be obtained , and these results are in much improved agreement with experiment. We also test the importance of core electron correlation on intensities, and find the effect to be negligible. Of the existing water dipole moment functions in the literature, the present one is the most accurate. (C) 2000 American Institute of Physics. [S0021-9606(00)30440-8].