A transferable valence force field for polyatomic molecules: A scheme for a series of molecules containing CO groups

Abstract

The definition of a transferable valence force field is given for a series of molecules containing CO groups, including pyruvic acid, acetone, acetic acid, methyl acetate, formic acid and methyl formate. Its main characteristics might be applied to any other molecule or group of molecules. The limitation of the force fields through transferability requirements opens expectations for a strong data reduction. A set of 144 force constants is adjusted to 308 frequencies and 232 shifts of 61 isotopic modifications. The good fit achieved (rms-deviation: 6.38 and 1.26 cm −1 for frequencies and shifts, respectively) suggests the present type of constraining to be very valuable. Furthermore, systematic trends concerning magnitudes and signs of distinct types of force constants as well as good agreement with ab initio values in the case of formic acid indicate physical significance. A PED-characterization of the fundamentals of the main parent species is given. In the case of methyl acetate the calculations suggest a revision of published assignments.