The Measurement of Bond Moments and Derivatives in HCN and DCN from Infrared Intensities

The absolute infrared absorption intensities of the fundamental vibrations of HCN and DCN have been measured, using the pressure broadening technique. These measurements yield the bond moments μC–H=±1.13d, μC≡N=±1.80d and show that if C is positive in the C≡N dipole, H is positive in the C–H dipole. The change in moment with internuclear distance is found to be ∂μ/∂rC–H=±1.05d/A, ∂μ/∂rC≡N=∓0.66d/A. Two of the three anomalous peaks in the band ν1 of HCN are shown to arise from the dimer of HCN.