Nuclear Quadrupole Interaction in HCN and DCN in the Bending Vibrational Mode

The ΔJ=0, ΔF=0 transition in HCN and DCN in an excited bending mode of vibration was observed to possess structure due to an asymmetry in the electric field gradient at the nitrogen nucleus coupling to the quadrupole moment of that nucleus. A selective breaking of the π bond perpendicular to the plane of bending when the molecule assumes its ionic structure is suggested as the source of the asymmetry.