We report on the determination of a high quality ab initio potential energy surface ͑PES͒ and dipole moment function for water. This PES is empirically adjusted to improve the agreement between the computed line positions and those from the HITRAN 92 data base with Jр5 for H 2 16 O. The changes in the PES are small, nonetheless including an estimate of core ͑oxygen 1s) electron correlation greatly improves the agreement with the experiment. Using this adjusted PES, we can match 30 092 of the 30 117 transitions in the HITRAN 96 data base for H 2 16 O with theoretical lines. The 10, 25, 50, 75, and 90 percentiles of the difference between the calculated and tabulated line positions are Ϫ0.11, Ϫ0.04, Ϫ0.01, 0.02, and 0.07 cm Ϫ1. Nonadiabatic effects are not explicitly included. About 3% of the tabulated line positions appear to be incorrect. Similar agreement using this adjusted PES is obtained for the 17 O and 18 O isotopes. For HD 16 O, the agreement is not as good, with a root-mean-square error of 0.25 cm Ϫ1 for lines with Jр5. This error is reduced to 0.02 cm Ϫ1 by including a small asymmetric correction to the PES, which is parameterized by simultaneously fitting to HD 16 O and D 2 16 O data. Scaling this correction by mass factors yields good results for T 2 O and HTO. The intensities summed over vibrational bands are usually in good agreement between the calculations and the tabulated results, but individual line strengths can differ greatly. A high-temperature list consisting of 307 721 352 lines is generated for H 2 16 O using our PES and dipole moment function.

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.

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The structure and binding energies are determined for many of the M(H2O)+n and M(H2O)2+n species, for n=1–3 and M=Mg, Ca, or Sr. The trends are explained in terms of metal sp or sdσ hybridization and core polarization. The M(NH3)+n systems, with M=Mg or Sr, are also studied. For the positive ions, the low-lying excited states are also studied and compared with experiment. The calculations suggest an alternative interpretation of the SrNH+3 spectrum.

Theoretical studies of the first and secondrow transitionmetal mono and dicarbonyl positive ions J. Chem. Phys. 93, 609 (1990); 10.1063/1.459508 Positive ions of the first and secondrow transition metal hydrides J. Chem. Phys. 87, 481 (1987); 10.1063/1.453594Theoretical spectroscopic parameters for the lowlying states of the secondrow transition metal hydridesThe metal-carbon bond dissociation energies (Do) and geometries for the first-and secondrow transition-metal methyl neutrals and positive ions are determined. The computed Do values for the positive ions compare favorably with experiment, except for RuCH3+ , RhCH 3 + , and PdCH 3 + where the experimental values are 10--15 kcallmollarger. The computed Do values for the hydride and methyl positive ions are similar for all metals in both transition rows except for Cu and Ag. However, for the neutral systems the Do values for the methyls are smaller, especially on the right-hand side of both transition rows where the differences approach 15 kcallmol. In general, the dissociation energies do not follow simple trends, as the individual Do values are significantly affected by the relative spacings between the atomic states of the metal. The study of all of the methyl neutral and ions of both transition rows presented here provides a consistent set of data for the dissociation energies, thereby allowing a critical assessment of the experimental data for these molecular species, and an enhanced understanding of the different bonding mechanisms.