INFRARED TRANSITION INTENSITIES FOR WATER - A COMPARISON OF AB-INITIO AND FITTED DIPOLE-MOMENT SURFACES

Four surfaces giving the dipole moment for water as a function of internuclear separations are compared. These surfaces are used to predict intensities for transitions involving J = 0 - 1 and Q-branch transitions for J = 5 and 10. These intensities are compared with observed transition intensities for (H2O)-O-16 from the HITRAN database. For reasons of computational efficiency these calculations were performed with a new discrete variable representation (DVR) transition intensity program, DIPOLE3. Our comparisons suggest that the recent ab initio dipole moment surfaces of Gabriel el al. (J. Chem. Phys. 99, 897-900 (1993)) is the most reliable. These surfaces give accurate linestrengths for transitions whose intensity vary by nine orders of magnitude and promise good extrapolation properties. The calculations also point to a number of transitions which differ significantly from the values tabulated in HITRAN. (C) 1995 Academic Press, Inc.