Normal mode analysis of 2,2′-bipyridine—II. Crystal vibrations

Abstract A normal mode analysis of the crystal spectrum of 2,2′-bipyridine was carried out using a previously determined intramolecular force field and an intermolecular potential described in terms of interactions among non-bonded atoms. New i.r. and Raman data in the region of lattice vibrations are presented, which can be satisfactorily accounted for by frequency calculations in the rigid-body approximation. Frequency splittings and shifts of internal modes, mixing with external vibrations and relative intensity of out-of-plane modes are analyzed through calculations at k = 0 which include all vibrational degrees of freedom.