Calculated Dipole-Moment Functions and the Infrared Intensities of HCN and N2O

Abstract

The dipole moments of HCN and N₂O are computed for different geometric configurations of these molecules, using the best available wavefunctions from the “near‐Hartree–Fock” calculations of McLean and Yoshimine. From these calculated dipole‐moment functions the derivatives with respect to the two stretching coordinates of each molecule are computed and compared with the experimental values obtained from infrared intensity measurements. The absolute magnitudes of the calculated derivatives for both HCN and N₂O agree reasonably well with the experimental values. The relative signs of the calculated derivatives, ${\mathrm{\partial \mu \hspace{0.17em}/\hspace{0.17em}\partial r}}_{\mathrm{NN}}$ and ${\mathrm{\partial \mu \hspace{0.17em}/\hspace{0.17em}\partial r}}_{\mathrm{NO}}$ , appear to be in agreement with experiment for NNO, whereas the relative signs calculated for ${\mathrm{\partial \mu \hspace{0.17em}/\hspace{0.17em}\partial r}}_{\mathrm{NH}}$ and ${\mathrm{\partial \mu \hspace{0.17em}/\hspace{0.17em}\partial r}}_{\mathrm{CN}}$ are not consistent with the experimental results for HCN. Possible reasons are suggested for this discrepancy, which appears to be more serious than the recent controversy regarding the sign of the CO dipole moment.