Knowledge Bank

Anharmonic vibrational wavefunctions have been calculated from empirically corrected ab initio potentials (SCF or CEPA) by a variational $method1$. Accurate electric dipole moment surfaces are obtained by the coupled electron pair approximation (CEPA) of $Meyer2$, the dipole moment being calculated as an energy derivative. Applications concern the IR intensities of stretching vibrations of linear molecules ($HCN3,HCP3,N2O,HCCF$, and $HC3N$) and the symmetric bending vibrations of $CH3$ and $NH3$. Isotope effects are discussed and the accuracy of the familiar ``double harmonic'' approximation is examined.