DYNAMICAL AND SPECTROSCOPIC STUDY OF INTERNAL-ROTATION IN FORMIC, THIOLFORMIC, THIONFORMIC AND DITHIOFORMIC ACIDS USING A REDUCED POTENTIALMODEL

The torsional nu(9) frequencies and relative intensities are determine d for formic, thiolformic, thionformic and dithioformic acids by using two essentially different approaches for the potential energy functio ns. The first approach consists in calculating 19 energy points along the torsional coordinate and fitting them to a Fourier expansion in te rms of cosine functions. The second approach consists in using a reduc ed formula for the potential which needs only four energy points. The kinetic functions are deduced accordingly. Relatively small deviations are found in the spectra between both approaches. Structural, dynamic al and spectroscopic properties between the four acids are also discus sed. Finally, the theoretical results are compared with the available experimental data. It is concluded that the reduced approach can be ad vantageously used especially in multivariable problems in which the st andard approach will be too expensive in terms of computer time, (C) 1 998 Elsevier Science B.V.