VIBRATIONAL ANALYSIS AND MOLECULAR-STRUCTURE OF BIPYRAZINE

A complete vibrational analysis of bipyrazine is presented, based on I R and Raman data and on the predictions of a valence force field initi ally transferred from 2,2'-bypirimidine. A set of refined force consta nts, obtained from the experimental data of both molecules, is also pr oposed to improve the agreement with observed data for the out-of-plan e modes. Both experimental data and calculation suggest a centro-symme tric, trans planar conformation for bipyrazine. The vibrational assign ment is discussed in terms of the kinetic energy distribution which, u nlike the procedure based on the potential energy, is not influenced b y numerical values of frequencies and force constants and allows unamb iguous identification of normal modes in which each ring moves as a wh ole. Different frequency shifts for ring vibrations are predicted, for a model related to bipyrazine adsorbed to a metallic substrate throug h a nitrogen atom, in ortho or meta position relative to the inter-rin g bond.