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

Abstract

In general, when computing intensities for polyatomics, one has to interpolate the dipole moment function obtained from ab initio calculations. For some high overtones of the water molecule, the computed intensities can be very sensitive to the way in which the interpolation is done. Our previous analytic 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.

Fourier transform measurements of water vapor line parameters in the 4200–6600cm−1 region

“…An excellent agreement is obtained (see Fig. 5) with the data of Mikhailenko et al The calculated values refer to the calculation using the potential energy surface and the pure ab initio dipole moment surfaces of Partridge and Schwenke [46]. [19,60] (panel b) obtained from Giessen spectra.…”

“…However, the intensities of Toth are systematically lower than ours, whereas those of Mikhailenko et al [19,60], obtained from Giessen spectra are systematically higher. This important remark is to be correlated with the validation of the absolute intensities, particularly in the HITRAN database, confirmed through a comparison with the theoretical PS line lists based on variational calculations using pure ab initio dipole moment surfaces [46] and on the potential energy surface from [45] as cited before (see the next section for more details).…”

“…It is seen that a progress compared to HITRAN has been mainly achieved for H 2 16 O and HDO. These 10161 water transitions are shown band by band in Table 3 Rovibrational assignment of water lines is based on experimental energy levels known from previous studies and on global variational predictions of line positions and intensities [45,46]. The validation of the assignments and the determination of the experimental energy levels and their uncertainties for all four species were performed by using the RITZ program [47], which was successfully applied in previous studies of water spectra [19,21,48].…”

“…3 where all the values are lower than 0.12 cm À1 increasing our confidence in the assignments. The calculated values refer to the calculation using the potential energy surface and the pure ab initio dipole moment surfaces of Partridge and Schwenke [46].…”

“…A general comparison between our new dataset with the most extended experimental data in this spectral range as well as with PS predictions based on an ab initio dipole moment function [45,46] is shown in Table 9 where the integrated band intensities (SS s ) for the different isotopologues and the number of corresponding lines are given. Despite the great number of lines in the present data set, the numerous newly measured weak lines provide a relatively small contribution to the integrated intensity, which is in very close agreement when compared to HITRAN [35].…”