And anharmonic force field

Table 11 Fit to data used in refining to the harmonic and anharmonic force field of Table 10 ...

Harmonic and Anharmonic Force Field Calculations Table 14 The pure bending potential function o/HaO and SO... 

Martin JML, Taylor PR. Benchmark ab initio thermochemistry of the isomers of di-imide, N2H2, using accurate computed structures and anharmonic force fields. Mol Phys 1999 96 681-692. 

Martin, J.M.L. Basis set convergence study of the atomization energy, geometry, and anharmonic force field of SO2 the importance of inner polarization functions, J. Chem. Phys. 1998,108, 2791. 

Harmonic force fields and harmonic frequencies of PHg were obtained by SCF MO [8,13,17] and CEPA calculations [8] for the transfer of force fields of other penta-coordinated molecules to PHg, see [26, 27]. A predicted IR gas-phase spectrum with rotational fine structure (at 300 K) is displayed in [17]. Anharmonicity constants and vibration-rotation interaction constants were derived from an anharmonic force field. From a scaling procedure, making use of harmonic and anharmonic force fields of PHg and PH3 (as reference molecule) the following wave numbers (in cm ) of the PHg fundamentals were predicted [18] (v = stretching, 6 = deformation, s = symmetric, as = antisymmetric, op = out-of-plane) ... 

As will be made clear in the followings sections, accurate equilibrium stmcture as well as harmonic and anharmonic force field computations are necessary in order to fulfill point (a), dipole moment evaluations for point (b), and, finally, accurate electric field gradient, spin-rotation, and spin-spin tensor calculations for point (c). Additionally, vibrational corrections for properties related to points (a) to (c) are often required. 

Accurate ab initio theoretical calculations of harmonic and anharmonic force fields of molecules as large as benzene have recently been performed. By comparing the experimentally determined molecular constants with the calculated ones, the reliability of theoretical calculations can be assessed. All the molecular constants of COF2 in Table 1 can be evaluated from the theoretical anharmonic force field. For molecules such as ammonia the computed fundamental wavenumbers are within 3 cm or better of the experiment. For anharmonic constants and centrifugal distortion constants, which are much smaller than the fundamental frequencies, the deviations are on average around 15%. The experimental determination of anharmonic constants x j that appear in the equation for the vibrational energy of a polyatomic molecule with the harmonic frequencies cop and without degenerate vibrations ... 

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